中央研究院 原子與分子科學研究所

In applications of silicon nanowire field-effect transistors (SiNW-FETs) as biosensors, the SiNW-FETs conventionally are all area modified (AAM), with receptors covering not only the minute SiNW surface area but also the relatively large surrounding substrate area. In this study, using a bottom-up technique, we successfully fabricated selective surface modified (SSM) SiNW-FETs with the receptors on the SiNW sensing surface only. In this approach, the strategy was to modify the SiNWs with a chemical linker of 3-aminopropyltrimethoxysilane (APTMS) prior to photolithographic fabrication of the device. The APTMS molecules modifying the SiNWs survived the harsh photolithographic processes, including coating with photoresist, washing with organic solvent, and thermal annealing. These SSM SiNW-FETs also exhibited desirable electrical characteristics such as ohmic contact and high transconductance. Using the biotin–avidin binding system, we showed that the faster response time and smaller sample requirements of the SSM SiNW-FETs, relative to the conventional AAM SiNW-FETs, clearly show that restricting the surface modification of the SiNW-FETs substantially improves their detection sensitivity.
Detection with a SSM boronic acid-modified SiNW-FET of the dopamine released under high-K⁺ buffer stimulation from living PC12 cells also demonstrates that SiNW-FETs can serve as highly sensitive biosensors for biomedical diagnosis. In binding affinity measurements with SiNW-FETs, the dissociation constants (Kd) of the biotin–avidin and dopamine–boronic acid complexes were determined to be 1571 fM and 3378 fM, respectively.

We present a chemical vapor deposition (CVD) method to catalytically synthesize large-area, transferless, single-to few-layer graphene sheets using hexamethyldisilazane
(HMDS) on a SiO₂/Si substrate as a carbon source and thermally evaporated alternating Ni/Cu/Ni layers as a catalyst. The as-synthesized graphenefilms were characterized by Raman
spectroscopic imaging to identify single- to few-layer sheets. This HMDS-derived graphene layer is continuous over the entire growth substrate, and single- to trilayer mixed sheets can be up to 30μm in the lateral dimension. With the synthetic CVD method proposed here, graphene can be grown into tailored shapes directly on a SiO₂/Si surface through vapor priming ofHMDS onto predefined photolithographic patterns. The transparent and conductive HMDS-derived graphene exhibits itspotential for widespread electronic and opto-electronic applications.

Understanding how proteins interact with each other is the basis for studying the biological mechanisms behind various physiological activities. Silicon nanowire field-effect transistors (SiNW-FETs) are sensitive sensors used to detect biomolecular interactions in real-time. However, the majority of the applications that use SiNW-FETs are for known interactions between different molecules. To explore the capability of SiNW-FETs as fast screening devices to identify unknown interacting molecules, we applied mass spectrometry (MS) to analyze molecules reversibly bound to the SiNW-FETs. Calmodulin (CaM) is a Ca²⁺- sensing protein that is ubiquitously expressed in cells and its interaction with target molecules is Ca²⁺- dependent. By modifying the SiNW-FET surface with glutathione, glutathione S-transferase (GST)-tagged CaM binds reversibly to the SiNW-FET. We first verified the Ca²⁺-dependent interaction between GST–CaM and purified troponin I, which is involved in muscle contraction, through the conductance changes of the SiNW-FET. Furthermore, the cell lysate containing overexpressed Ca²⁺/CaM-dependent protein kinase IIa induced a conductance change in the GST–CaM-modified SiNW-FET. The bound proteins were eluted and subsequently identified by MS as CaM and kinase. In another example, candidate proteins from neuronal cell lysates interacting with calneuron I (CalnI), a CaM-like protein, were captured with a GST–CalnImodified SiNW-FET. The proteins that interacted with CalnI were eluted and verified by MS. The Ca²⁺- dependent interaction between GST–CalnI and one of the candidates, heat shock protein 70, was reconfirmed via the SiNW-FET measurement. Our results demonstrate the effectiveness of combining MS with SiNW-FETs to quickly screen interacting molecules from cell lysates.

The plasma membrane of a cell not only works as a physical barrier but also mediates the signal relay between the extracellular milieu and the cell interior. Various stimulants may cause the redistribution of molecules, like lipids, proteins, and polysaccharides, on the plasma membrane and change the surface potential (Φ_s). In this study, the Φ_ss of PC12 cell plasma membranes were measured by atomic force microscopy in Kelvin probe mode (KPFM). The skewness values of the Φ_ss distribution histogram were found to be mostly negative,and the incorporation of negatively charged phosphatidylserine shifted the average skewness values to positive. After being treated with H₂O₂, dopamine, or Zn2⁺,phosphatidylserine was found to be translocated to the membrane outer leaflet and the averaged skewness values were changed to positive values. These results demonstrated that KPFM can be used to monitor cell physiology status in response to various stimulants with high spatial resolution.

A  silicon  nanowire  field-effect  transistor  (SiNW-FET)  coated  with  a  polyvinyl  chloride  (PVC)  membrane containing  valinomycin  (VAL)  was  employed  as  a  biosensor (referred  to  as  VAL-PVC/SiNW-FET)  to  detect the  K⁺-efflux  from  live  chromaffin  cells.  The  detection  sensitivity  of  K⁺ with  the  VAL-PVC/SiNW-FET  covers a  broad range  of  concentrations  from  10⁻⁶ to  10⁻²M.  The  apparent  association  constants  between  VAL and  Li⁺,  Na⁺,  K⁺,  and  Cs⁺ in  Tris  buffer  solution  were  determined to  be  67  ±  42,  120  ±  23,  5974  ±  115,  and 4121  ±  140  M⁻¹,  respectively.  By  culturing  chromaffin  cells  on  the  VAL-PVC/SiNW-FET,  the  conductance was significantly  increased  by  nicotine  stimulation  in  a  bath  buffer  without  Na⁺.  The  K⁺ concentration at  the  cell  surface  was  determined  to  be  ∼20  M  under  the  stimulation  of  5  mM  nicotine.  These  results demonstrate  that  the  VAL-PVC/SiNW-FET  is  sensitive  and  selective  to  detect  the  released  K⁺ from  cells
and  is  suitable  for  applications  in  cellular  recording  investigations.

A low-cost and green method of producing nanocrystalline silicon thin films is presented. Using a magnesiothermic reduction process, we have successfully converted the surface
of soda lime glass directly into silicon thinfilm. Furthermore, by varying reaction time, the amount of silicon produced in thin film form (or layer thickness) can be controlled. The
nanocrystalline silicon thinfilms on glass were characterized using scanning electron microscopy, energy dispersive spec-troscopy and Raman spectroscopy. Finally, the optical pro-perties of the thinfilms derived at different reaction times were also measured. The band gaps of the synthesized thin films were within the range of 2.3–2.5 eV.