NANO TTER pubs. acs org/AnolE Kinked p-n Junction Nanowire Probes for High Spatial Resolution Sensing and Intracellular recording Zhe Jiang, Quan Qing" Ping Xie, Ruixuan Gao, and Charles M. Lieber**. I,F Department of Chemistry and Chemical Biology and 'School of Engineering and Applied Science, Harvard University, Cambridge Massachusetts 02138, United States S Supporting Information ABSTRACt: Semiconductor nanowires and other semi- onducting nanoscale materials configured as field-effect transistors have been studied extensively as biological/chemical (bio/chem) sensors. These nanomaterials have demonstrated high-sensitivity from one- and two-dimensional sensors, n although the realization of the ultimate pointlike detector has not been achieved. In this regard, nanoscale p-n diodes are attractive since the device element is naturally localized near the junction, and while nanowire p-n diodes have been widely studied as photovoltaic devices, their applications as bio/chem ensors have not been explored. Here we demonstrate that p-n diode devices can serve as a new and powerful family of highly localized biosensor probes. Designed nanoscale axial p-n junctions were synthetically introduced at the joints of kink nanowires. Scanning electron microscopy images showed that the kinked nanowire structures were achieved, and electrical transport measurements exhibited rectifying behavior with well-defined turn-on in forward bias as expected for a p-n diode In addition, scanning gate microscopy demonstrated that the most sensitive region of these nanowires was localized near the kinked region at the p-n junction. High spatial resolution sensing using these p-n diode probes was carried out in aqueous solution using fluorescent charged polystyrene nanobeads. Multiplexed electrical measurements show well-defined single-nanoparticle detection, and experiments with simultaneous confocal imaging correlate directly the motion of the nanobeads with the electrical signals recorded from the p-n devices. In addition, kinked p-n junction nanowires configured as three-dimensional probes demonstrate the capability of intracellular recording of action potentials from electrogenic cells. These p-n junction kinked nanowire devices, which represent a new way of constructing nanoscale probes with highly localized sensing regions, provide from within living cells and issue 3 substantial opportunity in areas ranging from bio/chem sensing and nanoscale photon detection to three-dimensional recording KEYWORDS: Nanosensor, nanoprobe, nanobioelectronics, nanoelectronic device, diode enabled many advances in functional nanoelectronics, -9 p-n junctions can be synthetically encoded in axial and core/ and moreover, have opened-up unique opportunities at the shell nanowires, 423, 4 although only the photovoltaic proper interface between nanoelectronics and biological systems. ties of such nanojunctions have been thoroughly studied.3,+ For example, recent studies have shown that nanoscale field- Such p-n diodes have not yet been investigated as bio/chem ffect transistors(nanoFETs)can be synthetically encoded at the sensors. Here we report a successful synthetic integration of tips of kinked silicon nanowires. These kinked nanostructures p-n junction in the kinked silicon nanowire structure, and study can be readily configured as three-dimensional(3D) bioprobes, for the first time both experimentally and theoretically these which enabled recording intracellular action potentials from devices as highly localized electronic biosensors. In particular, beating cardiomyocytes in a minimally invasive manner. This we focus on the use of p-n junction kinked nanowire devices work represented the first demonstration of internalizing an for charge sensing down to the single nanoparticle level, and for active electronic probe, a transistor, which was comparable in size intracellular potential recording within live cells. to viruses and many biological macromolecules inside a cell Kinked p-n junction silicon nanowires(SiNWs)were While these studies open up a new paradigm for integrating synthesized by gold nanoparticle-catalyzed chemical-vapor- electronics with cells and tissue, they are also potentially limited deposition( CVD) process with doping and geometric control in that synthetic preparation of an ideal pointlike nanoFET detector is challenging Received: January 20, 2012 In this regard, nanoscale p-n diodes are attractive since the Revised: February 6, 2012 device element is naturally localized at the depletion region of Published: February 6, 2012 ACS Publications o 2012 American Chemical Society 1711 dxdoloro/o.102/nl300256r| Nano Lert.2012,12.1711-1716
Kinked p−n Junction Nanowire Probes for High Spatial Resolution Sensing and Intracellular Recording Zhe Jiang,†,§ Quan Qing,†,§ Ping Xie,† Ruixuan Gao,† and Charles M. Lieber*,†,‡ † Department of Chemistry and Chemical Biology and ‡ School of Engineering and Applied Science, Harvard University, Cambridge, Massachusetts 02138, United States *S Supporting Information ABSTRACT: Semiconductor nanowires and other semiconducting nanoscale materials configured as field-effect transistors have been studied extensively as biological/chemical (bio/chem) sensors. These nanomaterials have demonstrated high-sensitivity from one- and two-dimensional sensors, although the realization of the ultimate pointlike detector has not been achieved. In this regard, nanoscale p−n diodes are attractive since the device element is naturally localized near the junction, and while nanowire p−n diodes have been widely studied as photovoltaic devices, their applications as bio/chem sensors have not been explored. Here we demonstrate that p−n diode devices can serve as a new and powerful family of highly localized biosensor probes. Designed nanoscale axial p−n junctions were synthetically introduced at the joints of kinked silicon nanowires. Scanning electron microscopy images showed that the kinked nanowire structures were achieved, and electrical transport measurements exhibited rectifying behavior with well-defined turn-on in forward bias as expected for a p−n diode. In addition, scanning gate microscopy demonstrated that the most sensitive region of these nanowires was localized near the kinked region at the p−n junction. High spatial resolution sensing using these p−n diode probes was carried out in aqueous solution using fluorescent charged polystyrene nanobeads. Multiplexed electrical measurements show well-defined single-nanoparticle detection, and experiments with simultaneous confocal imaging correlate directly the motion of the nanobeads with the electrical signals recorded from the p−n devices. In addition, kinked p−n junction nanowires configured as three-dimensional probes demonstrate the capability of intracellular recording of action potentials from electrogenic cells. These p−n junction kinked nanowire devices, which represent a new way of constructing nanoscale probes with highly localized sensing regions, provide substantial opportunity in areas ranging from bio/chem sensing and nanoscale photon detection to three-dimensional recording from within living cells and tissue. KEYWORDS: Nanosensor, nanoprobe, nanobioelectronics, nanoelectronic device, diode The rational design and synthesis of nanomaterials have enabled many advances in functional nanoelectronics,1−9 and moreover, have opened-up unique opportunities at the interface between nanoelectronics and biological systems.2,10−21 For example, recent studies have shown that nanoscale fieldeffect transistors (nanoFETs) can be synthetically encoded at the tips of kinked silicon nanowires.2,5 These kinked nanostructures can be readily configured as three-dimensional (3D) bioprobes, which enabled recording intracellular action potentials from beating cardiomyocytes in a minimally invasive manner.2 This work represented the first demonstration of internalizing an active electronic probe, a transistor, which was comparable in size to viruses and many biological macromolecules inside a cell. While these studies open up a new paradigm for integrating electronics with cells and tissue, they are also potentially limited in that synthetic preparation of an ideal pointlike nanoFET detector is challenging. In this regard, nanoscale p−n diodes are attractive since the device element is naturally localized at the depletion region of the junction.22 A number of previous studies have shown that p−n junctions can be synthetically encoded in axial and core/ shell nanowires,3,4,23,24 although only the photovoltaic properties of such nanojunctions have been thoroughly studied.3,4 Such p−n diodes have not yet been investigated as bio/chem sensors. Here we report a successful synthetic integration of p−n junction in the kinked silicon nanowire structure, and study for the first time both experimentally and theoretically these devices as highly localized electronic biosensors. In particular, we focus on the use of p−n junction kinked nanowire devices for charge sensing down to the single nanoparticle level, and for intracellular potential recording within live cells. Kinked p−n junction silicon nanowires (SiNWs) were synthesized by gold nanoparticle-catalyzed chemical-vapordeposition (CVD) process with doping and geometric control Received: January 20, 2012 Revised: February 6, 2012 Published: February 6, 2012 Letter pubs.acs.org/NanoLett © 2012 American Chemical Society 1711 dx.doi.org/10.1021/nl300256r | Nano Lett. 2012, 12, 1711−1716
Nano letters adapted from our previous report. 25 Initially, boron-doped of 0.6 V in forward bias. These results are consistent wi p-type SiNWs were grown for 15 min at a calibrated growth previously studies of straight SiNWs with axial p-n junctions te of 0. 7 um/min. The reactor was evacuated for ca. 15 s, and In addition, measurements made on devices with two contacts then growth was continued using phosphine dopant to create (Supporting Information Figure S2)showed that no an n-type nanowire segme p-n junction metal/ SiNW Schottky barriers were present and allowed the 30 s, followed by a second cycle of reactor evacuation and estimation of the dopant concentrations. Specifically, the dopant continued growth using phosphine for ca. 15 min. Scanning concentrations of the p-arm and n-arm were estimated to be electron microscopy(SEM)images of the SINWs prepared in ca. 9 x 108 and 9 x 109cm-,respectively this way( Figure la)showed that the majority(90%)of the In a planar p-n diode device, the p-n junction is mostly buried beneath the surface and thus can only be partially gated with a top gate electrode. In contrast, the axial design of our kinked nanowires fully exposes the nanoscale p-n junction to external potential and enables a much more effective gate schematic band diagram change of the nanowire diode when a gate potential is applied at the p-n junction. The heavily doped p-and n-arms are not affected by the gate and the Fermi energy is pinned along the nanowire. When a negative potential applied, the electron energy levels in both the conduction band b and the valence band are raised(blue dashed lines in Figure 1c) As a result, the p-depletion region becomes more conductive while the n-depletion region less conductive. In the case of applying a positive potential, the opposite occurs. In order to estimate the overall gate response of our device, we assume that (1) the carrier concentration distribution in the depletion region is linear,(2)the depletion region can be approximated as a number of small segments, each of which can be treated as a V(volt) field-effect transistor with uniform doping, (3)the gate coupling doped is ideal, and(4)the width of the depletion region is the same the abrupt junction. In addition, the mobility along the nanowire nplify the calculation withou affecting the physics. It follows that the resistanc of the p- n junction can be expressed as△R∝△vn(NA∥N2 (ND)/ND](see Supporting Information), where AV is the change of the gate potential, and NA and Np are the dopant Figure 1. Design and controlled synthesis of kinked p-n nanowires. concentration of the p- and n-arms, respectively. When NA and (a)Representative SEM image of a kinked p-n SiNW with 120 tip Np are equal or comparable, the p-n junction will behave as an angle Scale bar, I Am Inset: Schematic of a kinked p-n nanowire ambipolar FET. However, when NA ND, the p-n junction will ith 120%tip angle. The blue and red lines designate the p-doped and doped arms, respectively.(b) Current vs voltage (I-v)data function as a p-type FET, and similarly, when NA > Np, the p-n recorded from a representative kinked p-n nanowire device. Inset Inction will function as an n-type. In our design, the doping SEM image of the device structure. Scale bar, 2 um.(c)Schematic level of the p-arm is ten times lower than the n-arm, thus the band diagram(black curves)and band diagram change of kinked p-n device is predicted to behave as a p-type FET nowires under gate potential. The blue and red dashed lines Tip-modulated scanning gate microscopy(tmSGM)was designate band diagram under negative and positive gate potentials used to identify directly the gate response and length-scale of respectively. Eo Ev, and Ep mark the position of the conduction band the sensitive regions in kinked p-n nanowire devices. Briefly, valence band, and Fermi energy, respectively conductive atomic force microscopy(AFM)tip was us 9 local gate to modulate the conductance of the kinked p kinked nanowires have a 120 angle between the two arms, nanowire junction. The conductance change was phase-locked which is consistent with our previous results that the abrupt to the vibration of the tip to enhance the spatial resolution, evacuation/resumption of feeding gases during the growth n-type SiNWs introduces a 1200 kink in high-yield. In addition, imposed over the topological image of the device. Representa- analysis of images showed that a small fraction (<10%)of the tive data(Figure 2a)show several key features. First, only kinked nanowires exhibited a 60 angle( Supporting Informa- the region close to the kink where the p-n junction was tion Figure S1), indicating that the switching between p-an synthetically defined showed clear gate response. Second, the orientation )albeit at a much lower yield. Here we focus on the than the n-depletion region(inset traces, Figure 2a).This result is consistent with our theoretical estimate using the calculated To assess the overall electrical characteristics of the kinked dopant concentration of the arms and implies that the device p-n nanowires, contacts(Cr/Pd/Cr 1.5/120/60 nm) were behavior is similar to a p-type FET. Third, the length of the defined on both arms by electron-beam lithography(EBL) and p-depletion region, which defines the spatial resolution of the metallization(inset, Figure 1b). Typical current versus device, was estimated from the full width at half-maximum ltage(I-v) data(figure 1b) show clear rectification with no( whm) of the conductance line profiles along the nanowire axis measurable current in reverse bias and an onset for current flow (inset traces, Figure 2a) and found to be 210 nm. while the 1712 dxdoloro/0.1021/l300256 rINgno Lett.2012,12,1711-1716
adapted from our previous report.5,25 Initially, boron-doped p-type SiNWs were grown for 15 min at a calibrated growth rate of 0.7 μm/min. The reactor was evacuated for ca. 15 s, and then growth was continued using phosphine dopant to create an n-type nanowire segment (forming the p−n junction) for 30 s, followed by a second cycle of reactor evacuation and continued growth using phosphine for ca. 15 min. Scanning electron microscopy (SEM) images of the SiNWs prepared in this way (Figure 1a) showed that the majority (>90%) of the kinked nanowires have a 120° angle between the two arms, which is consistent with our previous results that the abrupt evacuation/resumption of feeding gases during the growth of n-type SiNWs introduces a 120° kink in high-yield.5 In addition, analysis of images showed that a small fraction ( ND, the p−n junction will function as an n-type. In our design, the doping level of the p-arm is ten times lower than the n-arm, thus the device is predicted to behave as a p-type FET. Tip-modulated scanning gate microscopy (tmSGM)29 was used to identify directly the gate response and length-scale of the sensitive regions in kinked p−n nanowire devices. Briefly, a conductive atomic force microscopy (AFM) tip was used as a local gate to modulate the conductance of the kinked p−n nanowire junction.30 The conductance change was phase-locked to the vibration of the tip to enhance the spatial resolution,29 and the conductance map at different tip biases was superimposed over the topological image of the device. Representative data (Figure 2a) show several key features. First, only the region close to the kink where the p−n junction was synthetically defined showed clear gate response. Second, the p-depletion region gave 3−5 fold larger conductance change than the n-depletion region (inset traces, Figure 2a). This result is consistent with our theoretical estimate using the calculated dopant concentration of the arms and implies that the device behavior is similar to a p-type FET. Third, the length of the p-depletion region, which defines the spatial resolution of the device, was estimated from the full width at half-maximum (fwhm) of the conductance line profiles along the nanowire axis (inset traces, Figure 2a) and found to be 210 nm.30 While the Figure 1. Design and controlled synthesis of kinked p−n nanowires. (a) Representative SEM image of a kinked p−n SiNW with 120° tip angle. Scale bar, 1 μm. Inset: Schematic of a kinked p−n nanowire with 120° tip angle. The blue and red lines designate the p-doped and n-doped arms, respectively. (b) Current vs voltage (I−V) data recorded from a representative kinked p−n nanowire device. Inset: SEM image of the device structure. Scale bar, 2 μm. (c) Schematic band diagram (black curves) and band diagram change of kinked p−n nanowires under gate potential. The blue and red dashed lines designate band diagram under negative and positive gate potentials respectively. EC, EV, and EF mark the position of the conduction band, valence band, and Fermi energy, respectively. Nano Letters Letter 1712 dx.doi.org/10.1021/nl300256r | Nano Lett. 2012, 12, 1711−1716
Lette nanowire devices and potential reductions through, for example, improvements in junction quality and reduction of the surface defects Localized detection using our kinked p-n probes was first xplored in single nanoparticle sensing experiments. Specifi V.=+5V V.=5V substrate,was coupled to poly( dimethylsiloxane)(PDMs) microfluidic channel to control the solution flow over the devices. Conductance versus time traces recorded simulta- neously from two independent devices following the troduction of a 1.2 nm solut b solution of 100 nm diameter chargee fluorescent polystyrene nanobeads( Figure 3a) exhibit several b Figure 2. tmSGM and water-gate experiments of kinked p-n nanowire devices. (a) Superposition of tmSGM n AFM topographic images of a representative kinked p-n nanowire device under Vip of +5 V (left, scanning direction from top down)and -5V (right, scanning direction from bottom p), respectively. Scale bar, 0.5 Am. The blue/red arrows indicate the p-type and n-type depletion/ accumulation regions (left panel), respectively; the same positions show accumulation/depletion in the right panel Insets: line profiles of the tmSGM signal along the white dashed lines about these p-type and n-type regions. (b) Conductance versus water-gate reference potential data recorded from a representative kinked p-n nanowire device Ix phosphate buffer saline(PBS). Inset: schematic of conductance water"gate experiment. Figure 3. Fluorescent polystyrene nanobead sensing experiment. (a)(Left)Conductance vs time data recorded simultaneously from size of the sensitive region without optimization is comparable two independent kinked p-n nanowire devices with nanobeads in to the best value reported in our previous work, we note that deionized(Di)water introduced into the microfluidic channel. Black theoretical spatial resolution of a gated p-n device, charac- arrows mark the on/off points of the terized by the thickness of the depletion region, is 10-30 nm for lultaneously from the same two devices with highly doped silicon and thus could be improved in the future nly Di water in the microfluidic channel. (b)Schematic of fluorescent polystyrene nanobead sensing process using kinked p-n nanowire evices and the corresponding schematic of time-dependent change in fabricated through multiple EBL, metallization, and passivation evice conductance. Black arrows mark the on/off points of the signal. steps similar to previous reports, ,10, 12,26 using Cr/Pd/Cr for (c)(Top)Simultaneous confocal microscopy and conductance vs time data recorded from a kinked p-n nanowire device in a nanobead electrodes from the aqueous medium. The sensitivity of kinked solution flow. Red arrow marks the charge sensing signal. Blue arrow nanowire p-n devices in solution was assessed by water-gate xperiments"(inset, Figure 2b), where the p-n junction was P-n junction for images I and 2. The green arrows in the images highlight the positions of the nanowire junction and fluorescent forward biased at 1.0 V and a Ag/AgCl electrode was used to nanobead in both images. In Image 1, the two green arrows overlap control the chemical potential (vp) of the solution. Representa (Bottom) Simultaneous confocal microscopy and conductance vs time tive conductance versus Ve data (Figure 2b)demonstrate a D) demonstrate a data recorded from the same device without nanobeads in solution. p-type response and sensitivity of 620 nS/V. The p-type Blue arrows indicate photocurrent peaks due to the laser scanning ov esponse is consistent with the tmSGM results. The water-gate the p-n junction. The green arrow in the image highlights the position results also exhibit an increase in noise with increasing device f the nanowire junction. All the electrical data were filtered through a conductance, which could be due to increased recombination .00 Hz low-pass digital filter. Scale bars, 5 um at higher carrier concentrations within the depletion region. From a practical perspective, such water-gate data can be used to key features. First, when nanobeads choose an optimal operating regime (ie, where the sensitivity/ the device area, uncorrelated"pulse noise ratio is maximized), although future work should also observed from both devices(red trace address fundamental origin of noise in these p-n junction duration time of the"on"state of the 1713 dxdoloran0.1021/n300256 rI Nono Lett.2012.12.171-1716
size of the sensitive region without optimization is comparable to the best value reported in our previous work, we note that theoretical spatial resolution of a gated p−n device, characterized by the thickness of the depletion region, is 10−30 nm for highly doped silicon31 and thus could be improved in the future. The devices used for sensing experiments in solution were fabricated through multiple EBL, metallization, and passivation steps similar to previous reports,2,10,12,26 using Cr/Pd/Cr for contacts and SU8 as the passivation layer to isolate the metal electrodes from the aqueous medium. The sensitivity of kinked nanowire p−n devices in solution was assessed by water-gate experiments2,10 (inset, Figure 2b), where the p−n junction was forward biased at 1.0 V and a Ag/AgCl electrode was used to control the chemical potential (Vg) of the solution. Representative conductance versus Vg data (Figure 2b) demonstrate a p-type response and sensitivity of 620 nS/V. The p-type response is consistent with the tmSGM results. The water-gate results also exhibit an increase in noise with increasing device conductance, which could be due to increased recombination at higher carrier concentrations within the depletion region.22 From a practical perspective, such water-gate data can be used to choose an optimal operating regime (i.e., where the sensitivity/ noise ratio is maximized), although future work should also address fundamental origin of noise in these p−n junction nanowire devices and potential reductions through, for example, improvements in junction quality and reduction of the surface defects. Localized detection using our kinked p−n probes was first explored in single nanoparticle sensing experiments. Specifically, an array of kinked p−n nanowires probes on a SiO2 substrate2,10,12 was coupled to poly(dimethylsiloxane) (PDMS) microfluidic channel to control the solution flow over the devices.32 Conductance versus time traces recorded simultaneously from two independent devices following the introduction of a 1.2 nM solution of 100 nm diameter charged fluorescent polystyrene nanobeads (Figure 3a) exhibit several key features. First, when nanobeads solutions flow through the device area, uncorrelated “pulse” (on/off) signals were observed from both devices (red traces, Figure 3a). The time duration time of the “on” state of the pulses ranged from 50 to Figure 2. tmSGM and water-gate experiments of kinked p−n nanowire devices. (a) Superposition of tmSGM images on AFM topographic images of a representative kinked p−n nanowire device under Vtip of +5 V (left, scanning direction from top down) and −5 V (right, scanning direction from bottom up), respectively. Scale bar, 0.5 μm. The blue/red arrows indicate the p-type and n-type depletion/ accumulation regions (left panel), respectively; the same positions show accumulation/depletion in the right panel. Insets: line profiles of the tmSGM signal along the white dashed lines about these p-type and n-type regions. (b) Conductance versus water-gate reference potential data recorded from a representative kinked p−n nanowire device in 1× phosphate buffer saline (PBS). Inset: schematic of conductance vs water-gate experiment. Figure 3. Fluorescent polystyrene nanobead sensing experiment. (a) (Left) Conductance vs time data recorded simultaneously from two independent kinked p−n nanowire devices with nanobeads in deionized (DI) water introduced into the microfluidic channel. Black arrows mark the on/off points of the signals. (Right) Conductance vs time data recorded simultaneously from the same two devices with only DI water in the microfluidic channel. (b) Schematic of fluorescent polystyrene nanobead sensing process using kinked p−n nanowire devices and the corresponding schematic of time-dependent change in device conductance. Black arrows mark the on/off points of the signal. (c) (Top) Simultaneous confocal microscopy and conductance vs time data recorded from a kinked p−n nanowire device in a nanobead solution flow. Red arrow marks the charge sensing signal. Blue arrows mark the photocurrent peaks caused by the laser scanning over the p−n junction for images 1 and 2. The green arrows in the images highlight the positions of the nanowire junction and fluorescent nanobead in both images. In Image 1, the two green arrows overlap. (Bottom) Simultaneous confocal microscopy and conductance vs time data recorded from the same device without nanobeads in solution. Blue arrows indicate photocurrent peaks due to the laser scanning over the p−n junction. The green arrow in the image highlights the position of the nanowire junction. All the electrical data were filtered through a 100 Hz low-pass digital filter. Scale bars, 5 μm. Nano Letters Letter 1713 dx.doi.org/10.1021/nl300256r | Nano Lett. 2012, 12, 1711−1716
Nano letters 200 ms. Second, the conductance amplitudes of signals recorded PDMS on device-1(D1)and device-2(D2)were consistently 3-4 and 2-3 nS, respectively. The calibrated potential change(based on the water-gate sensitivity of the two devices) yields a consistent decrease of 5-6 mv at the p-n junction of both devices. This decrease in potential is also consistent with the negative charge on the nanobeads. Third, introduction of the aqueous solution without nanobeads(green traces, Figure 3a)exhibited no on/off pulsed signals from either device even over much longer ecording times. Together, these results are consistent with the detection of single nanobeads as outlined schematically in 9ns Figure 3b. Briefly, when there is no nanobead close to the p-n nin the del ning length, the conductance of the device remains constant (left image, Figure 3b). when a ches and/or attaches to the increase of conductance will be observed due to the negative charges on the nanobead3(middle image, Figure 3b),and when the nanobead leaves the sensitive region of the probe, the inductance returns to baseline(right image, Figure 3b). To confirm this interpretation of the multiplexed electrical measurements we carried out simultaneous confocal fluorescent 200ms microscopy imaging and electrical recording in the presence and absence of the fluorescent nanobeads. Significantly, we find that a conductance pulse(red arrow, Figure 3c) similar to that observed in measurements described above occurs when a single nanobead approaches the p-n junction at the elbow of the kink (inset-1)and then diffuses away(inset-2. The 50 ms wide Figure 4. Intracellular electrical recording from spontaneously beating conductance pulse is consistent with brief contact between the chicken cardiomyocytes. (a) Schematic of intracellular recording from nanobead and the p-n junction during this process. We also PDMS substrate using 3D kinked p-n note that when the laser scans over the p-n junction, there is a state intracellular recording using a 3D kinked p-n nanoprobes from a photocurrent(conductance increase)as indicated by blue spontaneously beating cardiomyocyte cell(Bottom)Zoom of the 3c), and this can be used to single action potential peak from the green-dashed region. the times when each image is captured. In addition, when the mc时 erm alized b y tbe cell in eddition we ind that th that conductance pulses correspond lo ts further confi p-n junction probes can be inserted and retracted multiple times from the same cell without losing key features of th detection and also highlight the potential of our p-n devi as pointlike nanoscale photodetectors for biophysical studi intracellular action potential or loss of cell viability, highlighting the minimal invasiveness of these nanoscale probes. We note We have also configured the kinked p-n junction nanowires hat the highly localized nature of our p-n kinked probe could enable detailed studies of the potential distribution within the interaction with living cells( Figure 4a). The 3D p-n junction cell and in subcellular structures. However, the current probe studies to yield nanowire probe oriented at 45-60 angle position for such experiments due to the flexibility of the with respect to the substrate. In a typical experiment, the 3D floating PDMS cell substrate p-n junction nanowire probes were functionalized with In conclusion we have demonstrated for the first time that a ,2-dimyristoyl-sn-glycero-3-phosphocholine(DMPc) bilayer nanoscale axial p-n junction synthetically embedded in a kink and then embryonic chicken cardiomyocyte cells cultured on nanowire structure can be tuned to work as a highly localized PDMS sheet were positioned over a nanowire probe within field-effect sensor to detect charges down to a single nanoparticle a cell perfusion chamber. Representative conductance versus level and to record full intracellular signals of spontaneously time data recorded from a spontaneously beating cardiomyocyte beating cardiomyocyte cells. Compared to previously reported cell( Figure 4b Supporting Information Figure S3)initially nanoFET probes, this gateable p-n diode device represents show an approximately 20 mv shift as the probe transitions new family of nanoscale biosensor probes with several unique from the extracellular region to the intracellular rest potential, advantages, including(1)a highly localized sensing region that which is consistent with our previous studies, followed by the development of periodic spikes with the same frequency of the can be tuned simply by optimizing the doping levels of the overall cell contraction, and an amplitude, shape and time scale p- and n-arms, (2)the possibility of yielding different types of of individual peaks characteristic of the intracellular action field-effect sensors(i.e, p-type, n-type, and ambipolar) by tuning potential. Specifically, a reproducible fast onset of over 60 mv the relative doping ratio between the p-and n-arms, and (3)the increase in local potential is observed followed by a broad slow potential of using the p-n junction as a 3D nanoscale photo- return to baseline within 200 ms, which is consistent with the detector, for example, to study highly localized fluorescent events intracellular action potentials recorded using a patch clamp 35 when integrated within living cells and 1714 dxdoloran0.1021/n300256 rI Nono Lett.2012.12.171-1716
200 ms. Second, the conductance amplitudes of signals recorded on device-1 (D1) and device-2 (D2) were consistently 3−4 and 2−3 nS, respectively. The calibrated potential change (based on the water-gate sensitivity of the two devices) yields a consistent decrease of 5−6 mV at the p−n junction of both devices. This decrease in potential is also consistent with the negative charge on the nanobeads.33 Third, introduction of the aqueous solution without nanobeads (green traces, Figure 3a) exhibited no on/off pulsed signals from either device even over much longer recording times. Together, these results are consistent with the detection of single nanobeads as outlined schematically in Figure 3b. Briefly, when there is no nanobead close to the p−n junction within the Debye screening length, the conductance of the device remains constant (left image, Figure 3b). When a nanobead approaches and/or attaches to the p−n junction, an increase of conductance will be observed due to the negative charges on the nanobead33 (middle image, Figure 3b), and when the nanobead leaves the sensitive region of the probe, the conductance returns to baseline (right image, Figure 3b). To confirm this interpretation of the multiplexed electrical measurements we carried out simultaneous confocal fluorescent microscopy imaging and electrical recording in the presence and absence of the fluorescent nanobeads.32 Significantly, we find that a conductance pulse (red arrow, Figure 3c) similar to that observed in measurements described above occurs when a single nanobead approaches the p−n junction at the elbow of the kink (inset-1) and then diffuses away (inset-2). The 50 ms wide conductance pulse is consistent with brief contact between the nanobead and the p−n junction during this process. We also note that when the laser scans over the p−n junction, there is a photocurrent (conductance increase) as indicated by blue arrows 1 and 2 (Figure 3c), and this can be used to assign the times when each image is captured. In addition, when the same solution without fluorescent nanobeads was introduced into the device, only periodic photocurrent was observed (lower trace, Figure 3c). These control experiments further confirm that conductance pulses correspond to single nanobead detection and also highlight the potential of our p−n devices as pointlike nanoscale photodetectors for biophysical studies and imaging. We have also configured the kinked p−n junction nanowires as three-dimensional (3D) probes for highly localized interaction with living cells (Figure 4a). The 3D p−n junction devices were fabricated using procedures similar to our previous studies2 to yield nanowire probe oriented at 45−60° angle with respect to the substrate. In a typical experiment, the 3D p−n junction nanowire probes were functionalized with 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) bilayer and then embryonic chicken cardiomyocyte cells cultured on a PDMS sheet were positioned over a nanowire probe within a cell perfusion chamber.2,34 Representative conductance versus time data recorded from a spontaneously beating cardiomyocyte cell (Figure 4b; Supporting Information Figure S3) initially show an approximately 20 mV shift as the probe transitions from the extracellular region to the intracellular rest potential, which is consistent with our previous studies,2 followed by the development of periodic spikes with the same frequency of the overall cell contraction, and an amplitude, shape and time scale of individual peaks characteristic of the intracellular action potential. Specifically, a reproducible fast onset of over 60 mV increase in local potential is observed followed by a broad slow return to baseline within 200 ms, which is consistent with the intracellular action potentials recorded using a patch clamp.35 These results show that the nanoscale p−n diode sensor can be internalized by the cell. In addition, we find that these nanowire p−n junction probes can be inserted and retracted multiple times from the same cell without losing key features of the intracellular action potential or loss of cell viability, highlighting the minimal invasiveness of these nanoscale probes. We note that the highly localized nature of our p−n kinked probe could enable detailed studies of the potential distribution within the cell and in subcellular structures. However, the current probe design does not provide sufficient control of the probe-cell position for such experiments due to the flexibility of the floating PDMS cell substrate. In conclusion, we have demonstrated for the first time that a nanoscale axial p−n junction synthetically embedded in a kinked nanowire structure can be tuned to work as a highly localized field-effect sensor to detect charges down to a single nanoparticle level and to record full intracellular signals of spontaneously beating cardiomyocyte cells. Compared to previously reported nanoFET probes,2 this gateable p−n diode device represents a new family of nanoscale biosensor probes with several unique advantages, including (1) a highly localized sensing region that can be tuned simply by optimizing the doping levels of the p- and n-arms, (2) the possibility of yielding different types of field-effect sensors (i.e., p-type, n-type, and ambipolar) by tuning the relative doping ratio between the p- and n-arms, and (3) the potential of using the p−n junction as a 3D nanoscale photodetector, for example, to study highly localized fluorescent events when integrated within living cells and tissue. Figure 4. Intracellular electrical recording from spontaneously beating chicken cardiomyocytes. (a) Schematic of intracellular recording from spontaneously beating embryonic chicken cardiomyosytes cultured on PDMS substrate using 3D kinked p−n nanoprobes. (b) (Top) Steadystate intracellular recording using a 3D kinked p−n nanoprobes from a spontaneously beating cardiomyocyte cell. (Bottom) Zoom of the single action potential peak from the green-dashed region. Nano Letters Letter 1714 dx.doi.org/10.1021/nl300256r | Nano Lett. 2012, 12, 1711−1716
Nano letters ■ ASSOCIATED CONTENT (23)Gudlksen, M. S. Lauhon, L J; Wang, J; Smith, D. C; Lieber, S Supporting Information C.M. Nature2002,4l5,617-620. Additional information and figures. This material is available 2002, 420, 57-61 4)Lauhon, L.J; Gudlksen, M. S; Wang, D ;Lieber,C.M.Nature freeofchargeviatheInternetathttp://pubs.acs.org )Kinked silicon nanowires synthesized by chemical on( CVD)through a nanoparticle-catalyzed vapo ■ AUTHOR| NFORMATION Corresponding Author 00 nm diameter gold nano (Ted Pella) were dispersed on Si growth substrates with 600 nm SiO, layer(Nova Electronic Materials) was first carried out by Author Contributions owth of heavily boron-doped p-type SThese authors contributed equally to this work. eding SiH,(1 sccm), 60 sccm)into the system for 15 min at a total pressure of 40 Torr and Note temperature of 450C. The growth was then paused for 15 s by The authors declare no competing financial interest. rapidly evacuating the chamber to lowest pressure and shutting off the gas lines. SiH, ( scam,1000 Ppm in H2), and H2 ■ ACKNOWLEDGMENTS (60 sccm)were then flown into the system at the same total pressure C. M.L. acknowledges support of this research from a nIH the p-n junction. A second evaculation or bype section for 30 s, forming Director's Pioneer Award(1DP1OD003900) heavily doped n-type arm was allowed to finish in additional 15 min (26)Two pairs of metal electrodes(1.5 nm Cr/120 nm Pd/60 nn REFERENCES Cr, spacing between electrodes 1.5 pm)were fabricated on each of the (1)Timko, B P; Cohen-Kami, T; Qing, Q; Tian, B Lieber, C.M.IEEE P- and n-type arms of a kinked nanowire device. The diameter of the Trans. Nanotechnol. 2009, DOI: DOL: 10.1109/TNANO 2009.2031807 nanowire was 100 nm. The doping levels of the arms were estimated (2)Tian, B. Cohen-Karni, T. Qing, Q; Duan, X; Xie, P; Lieber, using N=a/qu, where N is the doping level, a is the conductivity C.M. Science2010,329,830-834. alculated from the slope of the I-V trace in Supporting Information (3)Tian, B. Zheng X; Kempa, T. J; Fang, Y; Yu, N Yu, G Figure S2, q is the charge of an electron, and u is the mobility. Here we Huang, J; Lieber, C. M. Nature 2007, 449, 885-890 (4)Kempa, T. J Tian, B. Kim, D. R; Hu, J; Zheng, X. Lieber C.M. Nano Lett.2008,8,3456-3460. L. 2003, 3. 149-152. Wang. Da; Wang, w. U, Lieber, C. M. Nano (S)Tian, B; Xie, P. Kempa, T J; Bell,D.C.Lieber,CM.Nat (28)Rusu, A Bulucea, C. Proc. Rom. Acad. 2009, 10, 285-290. Nanotechnol. 2009, 4, 824-829. (29)Wilson, N R; Cobden, D H Nano Left. 2008, 8, 2161-216S (6)Xu, S; Qin, Y. Xu, C; Wei, Y; Yang, R; Wang, Z.L.Nat. (30)The device chip was mounted on a Bio Scope MultiMode SPM stage(Digital Instrument). A constant current of 250-700 nA was (7)Yan, H; Choe, H. S. Nam, S. W; Hu, Y; Das, S. Klemic, ]. F; injected into the kinked p-n device, resulting in a forward bias of Ellenbogen, J. C. Lieber, C. M. Nature 2011, 470, 240-244 ( 8)Dick, KA; Deppert, K; Larsson, M W; Martensson, T; Seifert, differential preamplifier(SRS60, Stanford Research Systems).A W; Wallenberg, L. R; Samuelson, L. Nat. Mater. 2004, 3, 380-384 onductive AFM tip(ARROW-CONTPT-10, Nano World) vibrating at a resonance frequency of 90 kHz was used as a local gate and L: Lieber. c.m. proc. natl. acad. sci u... 2011. 108. 12212-12216 scanned over the device to map the conductance image in "Lift Mode (10)Qing, Q. Pal,.K Tian, B Duan, X; Timko, B. P Cohen. Specifically, first for each scan line zero potential was applied to the tip, Karni, T. Murthy, V. N Lieber, C. M. Proc. Natl Acad. Sci. U.S.A. and a topographic image was acquired in Tapping Mode with feedback 2010,107,1882-1887 nabled. The tip was then lifted up 30 nm, and a tip potential of +5 Vwas (11)Cohen-Karni, T; Timbo, B P. Weiss, L E; Lieber, C.M. Proc. applied. The tip was scanned across the same line again following the Natl. Acad.sai.U.SA.2009,106,7309-7313 captured topologica with feedback turned off, when the change of (12)Cohen-Karni, T. Qing, Q; Li,Q; Fang,Y; Lieber,C.MNano oltage across the device was recorded with a lock-in amplifie Let2010,10,1098-1102 Stanford Research Systems) using the tip oscillation as the reference (13)Heller, I; Smaal, W TT; Lemay, S G Dekker, C. Small 2009, frequency. In order to remove the drift error during the imaging, we scanned in opposite directions for V. (14)Kotov, N. A; Winter, JO; Clements, I P Jan, E, Timk ,B. 2i0 nm as the corrected length of the sensitive region for our device. Vup =-5 V(fwhm 300 nm) images and obtained the average of P. Campidelli, S. Pathak, S. Mazzatenta, A- Lieber, C M. Prato, M j Bellamkonda, R V; Silva, G A; Kam, N. W.S. Patolsky, F; Ballerini, (31)Weber, L Gmelin, E. ApPL. Phys. A 1991,53, 136-140 LAdv. Mater.2009,21,3970-4004 (32)To control the solution flowing over the devices, a 1.7 mm thick (15)Patolsky, F; Timko, B. P Yu, G; Fang, Y. Greytak, A.B polydimethylsiloxane(PDMS)sheet with a microfluidic channel Zheng, G. Lieber, C. M. Science 2006, 313, 1100-ll0 50 um in height and 1 mm in width was put on the device chip (16)Lieber, C. M. MRS Bull. 2011, 36, 1( Fluorescent polystyrene nanobeads of 100 nm in diameter(initial (17)Patolsky, F. Timko, B P. Zheng, G.F Lieber, C M. MRS Bull concentration 24 nM in DI water, excitation wavelength 540 nm, 2007,32,142-149 mission wavelength 560 nm, from Phosphorex) were diluted in DI (18) Timko, B. P: Cohen-Karni, T 8 water(1: 20)and introduced into the microfluidic channel at a flow er, C. M. Nano Lett. 2009,, 914-918 rate of 0.02 mL/hour set by a syringe pump(PHD 2000, Harvard T.S. Agarwal, A; Ye, F; Balasubramanian, N; Chen, P. Apparatus). A confocal fluorescent microscope(FV1000, Olymp Small2009,S,208-212. was used to image the motion of the fluorescent nanobeads and the (20)Eschermann, J. F; Stockmann, R; Hueske, M; Vu, X. T; kinked probes in real time while the conductance was recorded. Real brandt, S. Offenhausser, A. AppL. Phys. Lett. 2009, 95, 083703-1 time fluorescent images of unction area were captured at a 083703-3. te of 2 hz a 559 nm laser to excite the nanobeads. Two (21)Stern, E; Klemic, J. F; Routenberg, D. A; Wyrembak, P.N hannels with filters of 490-540 nm and 575-675 nm were recorded Turner-Evans, D. B; Hamilton, A. D. LaVan, D. A Fahmy, T. M; together to rule out noise signals and unambiguously identify the Reed,M. A. Nature2007,445,519-522 anobeads. Images were then superimposed over the device image (22)Sze, S. M. Semiconductor devices, physics and technology: wiley: recorded with a 535-565 nm filter to mark the relative position of the apore, 2002; Pp nanobeads and the p-n junction. 1715 dxdoloro/0.1021/l300256 rINgno Lett.2012,12,1711-1716
■ ASSOCIATED CONTENT *S Supporting Information Additional information and figures. This material is available free of charge via the Internet at http://pubs.acs.org. ■ AUTHOR INFORMATION Corresponding Author *E-mail: cml@cmliris.harvard.edu. Author Contributions § These authors contributed equally to this work. Notes The authors declare no competing financial interest. ■ ACKNOWLEDGMENTS C.M.L. acknowledges support of this research from a NIH Director’s Pioneer Award (1DP1OD003900). ■ REFERENCES (1) Timko, B. P.; Cohen-Karni, T.; Qing, Q.; Tian, B.; Lieber, C. M. IEEE Trans. Nanotechnol. 2009, DOI: DOI:10.1109/TNANO.2009.2031807. (2) Tian, B.; Cohen-Karni, T.; Qing, Q.; Duan, X.; Xie, P.; Lieber, C. M. Science 2010, 329, 830−834. (3) Tian, B.; Zheng, X.; Kempa, T. J.; Fang, Y.; Yu, N.; Yu, G.; Huang, J.; Lieber, C. M. Nature 2007, 449, 885−890. (4) Kempa, T. J.; Tian, B.; Kim, D. R.; Hu, J.; Zheng, X.; Lieber, C. M. Nano Lett. 2008, 8, 3456−3460. (5) Tian, B.; Xie, P.; Kempa, T. J.; Bell, D. C.; Lieber, C. M. Nat. Nanotechnol. 2009, 4, 824−829. (6) Xu, S.; Qin, Y.; Xu, C.; Wei, Y.; Yang, R.; Wang, Z. L. Nat. Nanotechnol. 2010, 5, 366−373. (7) Yan, H.; Choe, H. S.; Nam, S. W.; Hu, Y.; Das, S.; Klemic, J. F.; Ellenbogen, J. C.; Lieber, C. M. Nature 2011, 470, 240−244. (8) Dick, K. A.; Deppert, K.; Larsson, M. W.; Martensson, T.; Seifert, W.; Wallenberg, L. R.; Samuelson, L. Nat. Mater. 2004, 3, 380−384. (9) Jiang, X.; Tian, B.; Xiang, J.; Qian, F.; Zheng, G.; Wang, H.; Mai, L.; Lieber, C. M. Proc. Natl. Acad. Sci. U.S.A. 2011, 108, 12212−12216. (10) Qing, Q.; Pal, S. K.; Tian, B.; Duan, X.; Timko, B. P.; CohenKarni, T.; Murthy, V. N.; Lieber, C. M. Proc. Natl. Acad. Sci. U.S.A. 2010, 107, 1882−1887. (11) Cohen-Karni, T.; Timbo, B. P.; Weiss, L. E.; Lieber, C. M. Proc. Natl. Acad. Sci. U.S.A. 2009, 106, 7309−7313. (12) Cohen-Karni, T.; Qing, Q.; Li, Q.; Fang, Y.; Lieber, C. M. Nano Lett. 2010, 10, 1098−1102. (13) Heller, I.; Smaal, W. T. T.; Lemay, S. G.; Dekker, C. Small 2009, 5, 2528−2532. (14) Kotov, N. A.; Winter, J. O.; Clements, I. P.; Jan, E.; Timko, B. P.; Campidelli, S.; Pathak, S.; Mazzatenta, A.; Lieber, C. M.; Prato, M.; Bellamkonda, R. V.; Silva, G. A.; Kam, N. W. S.; Patolsky, F.; Ballerini, L. Adv. Mater. 2009, 21, 3970−4004. (15) Patolsky, F.; Timko, B. P.; Yu, G.; Fang, Y.; Greytak, A. B.; Zheng, G.; Lieber, C. M. Science 2006, 313, 1100−1104. (16) Lieber, C. M. MRS Bull. 2011, 36, 1052−1063. (17) Patolsky, F.; Timko, B. P.; Zheng, G. F.; Lieber, C. M. MRS Bull. 2007, 32, 142−149. (18) Timko, B. P.; Cohen-Karni, T.; Yu, G.; Qing, Q.; Tian, B.; Lieber, C. M. Nano Lett. 2009, 9, 914−918. (19) Pui, T. S.; Agarwal, A.; Ye, F.; Balasubramanian, N.; Chen, P. Small 2009, 5, 208−212. (20) Eschermann, J. F.; Stockmann, R.; Hueske, M.; Vu, X. T.; Ingebrandt, S.; Offenhausser, A. ̈ Appl. Phys. Lett. 2009, 95, 083703−1− 083703−3. (21) Stern, E.; Klemic, J. F.; Routenberg, D. A.; Wyrembak, P. N.; Turner-Evans, D. B.; Hamilton, A. D.; LaVan, D. A.; Fahmy, T. M.; Reed, M. A. Nature 2007, 445, 519−522. (22) Sze, S. M. Semiconductor devices, physics and technology; Wiley: Singapore, 2002; pp 84−130. (23) Gudlksen, M. S.; Lauhon, L. J.; Wang, J.; Smith, D. C.; Lieber, C. M. Nature 2002, 415, 617−620. (24) Lauhon, L. J.; Gudlksen, M. S.; Wang, D.; Lieber, C. M. Nature 2002, 420, 57−61. (25) Kinked p−n silicon nanowires were synthesized by chemical vapor deposition (CVD) through a nanoparticle-catalyzed vapor− liquid−solid (VLS) process as described previously.5 Specifically, 100 nm diameter gold nanoparticles (Ted Pella) were dispersed on Si growth substrates with 600 nm SiO2 layer (Nova Electronic Materials). Growth of heavily boron-doped p-type arm was first carried out by feeding SiH4 (1 sccm), B2H6 (10 sccm, 100 ppm in H2), and H2 (60 sccm) into the system for 15 min at a total pressure of 40 Torr and temperature of 450 °C. The growth was then paused for 15 s by rapidly evacuating the chamber to lowest pressure and shutting off the gas lines. SiH4 (1 sccm), PH3 (4 sccm, 1000 ppm in H2), and H2 (60 sccm) were then flown into the system at the same total pressure and temperature to grow a heavily doped n-type section for 30 s, forming the p−n junction. A second evaculation of 15 s followed, and finally the heavily doped n-type arm was allowed to finish in additional 15 min. (26) Two pairs of metal electrodes (1.5 nm Cr/120 nm Pd/60 nm Cr, spacing between electrodes 1.5 μm) were fabricated on each of the p- and n-type arms of a kinked nanowire device. The diameter of the nanowire was 100 nm. The doping levels of the arms were estimated using N = σ/qμ, where N is the doping level, σ is the conductivity calculated from the slope of the I−V trace in Supporting Information Figure S2, q is the charge of an electron, and μ is the mobility. Here we take μ as 14 cm2 /V·s.27 (27) Cui, Y.; Zhong, Z.; Wang, D.; Wang, W. U.; Lieber, C. M. Nano Lett. 2003, 3, 149−152. (28) Rusu, A.; Bulucea, C. Proc. Rom. Acad. 2009, 10, 285−290. (29) Wilson, N. R.; Cobden, D. H. Nano Lett. 2008, 8, 2161−2165. (30) The device chip was mounted on a BioScope MultiMode SPM stage (Digital Instrument). A constant current of 250−700 nA was injected into the kinked p−n device, resulting in a forward bias of ∼1 V. The voltage drop across the device was measured using a low-noise differential preamplifier (SR560, Stanford Research Systems). A conductive AFM tip (ARROW-CONTPT-10, NanoWorld) vibrating at a resonance frequency of 90 kHz was used as a local gate and scanned over the device to map the conductance image in “Lift Mode”. Specifically, first for each scan line zero potential was applied to the tip, and a topographic image was acquired in Tapping Mode with feedback enabled. The tip was then lifted up 30 nm, and a tip potential of ±5 V was applied. The tip was scanned across the same line again following the captured topological profile with feedback turned off, when the change of voltage across the device was recorded with a lock-in amplifier (SR830, Stanford Research Systems) using the tip oscillation as the reference frequency.29 In order to remove the drift error during the imaging, we scanned in opposite directions for Vtip = +5 V (fwhm = 120 nm) and Vtip = −5 V (fwhm = 300 nm) images and obtained the average of 210 nm as the corrected length of the sensitive region for our device. (31) Weber, L.; Gmelin, E. Appl. Phys. A 1991, 53, 136−140. (32) To control the solution flowing over the devices, a 1.7 mm thick polydimethylsiloxane (PDMS) sheet with a microfluidic channel 50 μm in height and 1 mm in width was put on the device chip. Fluorescent polystyrene nanobeads of 100 nm in diameter (initial concentration 24 nM in DI water, excitation wavelength 540 nm, emission wavelength 560 nm, from Phosphorex) were diluted in DI water (1:20) and introduced into the microfluidic channel at a flow rate of 0.02 mL/hour set by a syringe pump (PHD 2000, Harvard Apparatus). A confocal fluorescent microscope (FV1000, Olympus) was used to image the motion of the fluorescent nanobeads and the kinked probes in real time while the conductance was recorded. Realtime fluorescent images of the p−n junction area were captured at a rate of 2 Hz using a 559 nm laser to excite the nanobeads. Two channels with filters of 490−540 nm and 575−675 nm were recorded together to rule out noise signals and unambiguously identify the nanobeads. Images were then superimposed over the device image recorded with a 535−565 nm filter to mark the relative position of the nanobeads and the p−n junction. Nano Letters Letter 1715 dx.doi.org/10.1021/nl300256r | Nano Lett. 2012, 12, 1711−1716
o Letters 33)The zeta potential of the nanobeads was measured using PALS Zeta Potential Analyzer(Brookhaven Instruments). An averaged potential of-59* ll mv from 6 runs was obtained. (34) Embryonic chicken cardiomyocytes were cultured using published protocols on thin PDMS films. 2, Device chips were ncubated with lipid vesicles of 1, 2-dimyristoyl-sn-ghy holine(DMPC, Avanti Polar Lipids Inc ) containing 1% 1-myristoyl glycero-3-Phosphocholine(NBD-lipid, Avanti Polar Lipids Inc )as fluorescent reporter to form lipid bilayers over the nanowire surface, using a procedure described earlier. The cell recording measurements were carried out in Tyrode solution(Sigma Aldrich) at 35C.The devices were forward biased at 1.0V, and the current was converted to oltage with a current preamplifier(Model 1211, DL Instruments)at nsitivity of 10- A/V, before low-pass filtered(0-6 kHz, CyberAmp 380, Molecular Devices)and digitized at 20 kHz sampling rate(Axor Digi1440A, Molecular Devices). A Ag/AgCl reference electrode was used to fix the extracellular solution potential at a constant value of +0.3V in all recording experiments anipulated using a glass micropipette mounted on a micromanipulator MP285, Sutter Instrument)to control the relative position between the cells and the nanowires as previously reported. (35)Zipes, D. P; Jalife, J. Cardiac Electrophysiology: From Cell to Bedside; Saunders: Philadelphia, 2009 1716 dxdoloro/0.1021/l300256 rINgno Lett.2012,12,1711-1716
(33) The zeta potential of the nanobeads was measured using PALS Zeta Potential Analyzer (Brookhaven Instruments). An averaged zeta potential of −59 ± 11 mV from 6 runs was obtained. (34) Embryonic chicken cardiomyocytes were cultured using published protocols on thin PDMS films.2,11 Device chips were incubated with lipid vesicles of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC, Avanti Polar Lipids Inc.) containing 1% 1-myristoyl- 2-{12-[(7-nitro-2−1,3-benzoxadiazol-4-yl) amino] dodecanoyl}-snglycero-3-phosphocholine (NBD-lipid, Avanti Polar Lipids Inc.) as fluorescent reporter to form lipid bilayers over the nanowire surface, using a procedure described earlier.2 The cell recording measurements were carried out in Tyrode solution (Sigma Aldrich) at 35 °C. The devices were forward biased at 1.0 V, and the current was converted to voltage with a current preamplifier (Model 1211, DL Instruments) at sensitivity of 10−6 A/V, before low-pass filtered (0−6 kHz, CyberAmp 380, Molecular Devices) and digitized at 20 kHz sampling rate (Axon Digi1440A, Molecular Devices). A Ag/AgCl reference electrode was used to fix the extracellular solution potential at a constant value of +0.3 V in all recording experiments.2,11 The PDMS/cell sheets were manipulated using a glass micropipette mounted on a micromanipulator (MP285, Sutter Instrument) to control the relative position between the cells and the nanowires as previously reported.2,11 (35) Zipes, D. P.; Jalife, J. Cardiac Electrophysiology: From Cell to Bedside; Saunders: Philadelphia, 2009. Nano Letters Letter 1716 dx.doi.org/10.1021/nl300256r | Nano Lett. 2012, 12, 1711−1716
