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.2012.12.171-1716200 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 photo￾detector, 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) Steady￾state 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