REPORTS detector of the overall probe. Scanning gate mi- sitivities of 4 to 8 S/. Similar sensitivities, 4 To further highlight the flexibility and ro- croscopy(SGM) measurements [fig. SI(19) to 8 uS/V, were observed for kinked nanowire bustness of the 3D nanoFET probes, we have showed that nanoscale FETs were integrated at devices fabricated on planar substrates, thus characterized the conductance and sensitivity in the probe tip during overall synthesis indicating that there is no degradation in the bent PBs as a glass micropipette was used to vary We have also examined the size limits of 3D configuration. We note that the sensitivity the tip height(Fig. 2C, inset). Typical data(Fig. these synthetic bioprobes in terms of the overall contribution from the lightly doped nanoFET is 2C) yield a <20-nS conductance change for a nanowire diameter and length L between kinks, >97% of the total device response. Localized de-- t10-um change in H, which corresponds to and we found that well-defined probe structures tection by the lightly doped region versus the <0.31% fluctuation in the total device conduct- are possible for values as small as -18 and 15 nm, heavily doped S/D nanowire arms is consistent ance. Likewise, the device sensitivity remains spectively( Fig. ID and fig. S2)(19). These with our SGM measurements on these acute- stable with a maximum change of -0.15 uS/or data show that it is possible to create active angle probes (fig. S1) and previous studies of 2.4%variation for this -+10-um tip-height change miconductor probes with dimensions smaller single-kinked nanowires (18). In addition, repetitive bending does not degrade than microtubules in cells(20) We next designed an unconventional nanoelectronic-device-fabrication approach that A would allow these probes to be used as cellular B probes. We made remote electrical interconne to the s/d nanowire arms on ultrathin sU-8 olymer ribbons above a sacrificial layer(Fig. 2A, top). The interfacial stress between mate- rials(21) was used to bend the probe upward After a final lift-off process(Fig 2A, bottom), see fig. S3A for fabrication details(19). Our nano- probes are distinct from previous nanoelectronic devices because (i) the FEt channel(Fig. 2A white dots)and S/D(Fig 2A, black segments) omponents are integrated epitaxially at the nand scale through synthesis(Fig. 1), similar to single- kink structures(18),() the nanoscale FEt is free-standing, and (iii) the acute-angle kinked- nanowire geometry and extended S/D arms spatially separate the functional nanoscale FET from the bulky interconnects by a distance up to -30 um, comparable to the size of single cells, that the nanoscale interrogation can be realized with minimum interference from mac- A representative SEM image of one free- tanding device(Fig 2B, D) demonstrates that the 60 kinked probe is intact after fabrication with the two nanowire arm terminals sand- wiched between the SU-8 polymer and the metal T contacts. We achieved >90% yields with 30 nanoprobe devices per chip. In addition, the probe height and angle(H and 8, Fig. 2A)were ystematically tuned by changing the length and thickness of the free-standing part of the metal interconnects/SU-8 backbone (fig. S3B)(9) We also found that the nanoprobe H and e typi cally increase when submerged in aqueous solu- tion[/e of the device(Fig 2B, I)are 25 um/430 and 38 um/90 in air and water, respectively Fig. 2B, Il and ID. This change is reversible and suggests that the nanoprobe devices an Time(s) intrinsically flexible, and moreover, that the ig. 3. Surface modification and specific orientation could be manipulated chem- Dark purple, light purple, pink, and ry (A) Schematics of nanowire probe entrance into a cell. ically(21). Last, free-standing 3D FET devices denote the phospholipid bilayers, heavily doped nanowire spectively. B)False-color fluorescence image of a lipid- have been stored in air for at least 8 months with- coated nanowire probe. DMPC was c 1% nitrobenzoxadiazole dye-labeled lipids and imaged out appreciable changes in nanoprobe orientations through a 510/21 band-pass filter (O) Differential interference contrast microscopy images (upper panels) and FET sensitivity and 3%a, respectively). and electrical recording (lower panel of an HL-1 cell and 60 kinked nanowire probe as the cell The sensitivity of the 3D nanoscale FET approaches (, contacts and internalizes(ID, and is retracted from (ID the nanoprobe. A pulled-glass probes was characterized in phosphate-buffered ropipette (inner tip diameter-5 um) was used to manipulate and voltage clamp the Hl-1 cell. The saline(PBS) solution(Fig. 2C and fig. S4A). dashed green line corresponds to the micropipette potential Scale bars, 5 um. (D)Electrical recording with Measurements of the conductance versus refer- a 60 kinked nanowire probe without phospholipids surface modification. Green and blue arrows in(O)and ence potential for the 3D probes yielded sen- (D)mark the beginnings of cell penetration and withdrawal, respectively 13AuguSt2010Vol329ScieNcewww.sciencemag.orgdetector of the overall probe. Scanning gate mi￾croscopy (SGM) measurements [fig. S1 (19)] showed that nanoscale FETs were integrated at the probe tip during overall synthesis. We have also examined the size limits of these synthetic bioprobes in terms of the overall nanowire diameter and length L between kinks, and we found that well-defined probe structures are possible for values as small as ~18 and 15 nm, respectively (Fig. 1D and fig. S2) (19). These data show that it is possible to create active semiconductor probes with dimensions smaller than microtubules in cells (20). We next designed an unconventional nanoelectronic-device–fabrication approach that would allow these probes to be used as cellular probes. We made remote electrical interconnects to the S/D nanowire arms on ultrathin SU-8 polymer ribbons above a sacrificial layer (Fig. 2A, top). The interfacial stress between mate￾rials (21) was used to bend the probe upward after a final lift-off process (Fig. 2A, bottom); see fig. S3A for fabrication details (19). Our nano￾probes are distinct from previous nanoelectronic devices because (i) the FET channel (Fig. 2A, white dots) and S/D (Fig. 2A, black segments) components are integrated epitaxially at the nano￾scale through synthesis (Fig. 1), similar to single￾kink structures (18), (ii) the nanoscale FET is free-standing, and (iii) the acute-angle kinked￾nanowire geometry and extended S/D arms spatially separate the functional nanoscale FET from the bulky interconnects by a distance up to ~30 mm, comparable to the size of single cells, so that the nanoscale interrogation can be realized with minimum interference from mac￾roscopic interconnects. A representative SEM image of one free￾standing device (Fig. 2B, I) demonstrates that the 60° kinked probe is intact after fabrication with the two nanowire arm terminals sand￾wiched between the SU-8 polymer and the metal contacts. We achieved ≥90% yields with ~30 nanoprobe devices per chip. In addition, the probe height and angle (H and q, Fig. 2A) were systematically tuned by changing the length and thickness of the free-standing part of the metal interconnects/SU-8 backbone (fig. S3B) (19). We also found that the nanoprobe H and q typi￾cally increase when submerged in aqueous solu￾tion [H/q of the device (Fig. 2B, I) are 25 mm/43° and 38 mm/90° in air and water, respectively (Fig. 2B, II and III)]. This change is reversible and suggests that the nanoprobe devices are intrinsically flexible, and moreover, that the specific orientation could be manipulated chem￾ically (21). Last, free-standing 3D FET devices have been stored in air for at least 8 months with￾out appreciable changes in nanoprobe orientations and FET sensitivity (<7 and 3%, respectively). The sensitivity of the 3D nanoscale FET probes was characterized in phosphate-buffered saline (PBS) solution (Fig. 2C and fig. S4A). Measurements of the conductance versus refer￾ence potential for the 3D probes yielded sen￾sitivities of 4 to 8 mS/V. Similar sensitivities, 4 to 8 mS/V, were observed for kinked nanowire devices fabricated on planar substrates, thus indicating that there is no degradation in the bent 3D configuration. We note that the sensitivity contribution from the lightly doped nanoFET is >97% of the total device response. Localized de￾tection by the lightly doped region versus the heavily doped S/D nanowire arms is consistent with our SGM measurements on these acute￾angle probes (fig. S1) and previous studies of single-kinked nanowires (18). To further highlight the flexibility and ro￾bustness of the 3D nanoFET probes, we have characterized the conductance and sensitivity in PBS as a glass micropipette was used to vary the tip height (Fig. 2C, inset). Typical data (Fig. 2C) yield a <20-nS conductance change for a ~T10-mm change in H, which corresponds to <0.31% fluctuation in the total device conduct￾ance. Likewise, the device sensitivity remains stable with a maximum change of ~0.15 mS/V or 2.4% variation for this ~T10-mm tip-height change. In addition, repetitive bending does not degrade Fig. 3. Surface modification and cellular entry. (A) Schematics of nanowire probe entrance into a cell. Dark purple, light purple, pink, and blue colors denote the phospholipid bilayers, heavily doped nanowire segments, active sensor segment, and cytosol, respectively. (B) False-color fluorescence image of a lipid￾coated nanowire probe. DMPC was doped with 1% nitrobenzoxadiazole dye–labeled lipids and imaged through a 510/21 band-pass filter. (C) Differential interference contrast microscopy images (upper panels) and electrical recording (lower panel) of an HL-1 cell and 60° kinked nanowire probe as the cell approaches (I), contacts and internalizes (II), and is retracted from (III) the nanoprobe. A pulled-glass micropipette (inner tip diameter ~ 5 mm) was used to manipulate and voltage clamp the HL-1 cell. The dashed green line corresponds to the micropipette potential. Scale bars, 5 mm. (D) Electrical recording with a 60° kinked nanowire probe without phospholipids surface modification. Green and blue arrows in (C) and (D) mark the beginnings of cell penetration and withdrawal, respectively. 832 13 AUGUST 2010 VOL 329 SCIENCE www.sciencemag.org REPORTS