(Invited) Nanowire Field-Effect Transistor-Based Biosensors as a Tool for Life Science

Silicon nanowire field-effect transistors (SiNW-FETs) have been used as a highly sensitive biosensor for label-free, real-time, and target selective detections in biomedical diagnosis and cellular-recording investigation. For practical uses, a reusable SiNW-FET was made possible with a reversible surface functionalization method, allowing for calibratable and quantitative analysis (Figure 1). In recent studies, we have applied SiNW-FETs for probing neurotransmitter release from living neurons, screening protein-protein interactions (Figure 2), detecting influenza virus, and monitoring extracellular K⁺ flux from stimulated chromaffin cells. In the study of protein-protein interactions, we integrated SiNW-FET with mass spectrometry (MS) for not only fast screening (by NW-FET) but also spectrally identifying (by MS) the unknown interacting proteins that were captured on the probe protein-modified SiNW-FET. To improve the sensitivity of SiNW-FETs, we designed a modification method to immobilize probe molecules only on the SiNW channel without contaminating the surrounding substrate, thus substantially enhancing the detection sensitivity. Recently, we developed an ultrasensitive biosensor for selective dopamine detection by an aptamer-modified multiple-parallel-connected (MPC) SiNW-FET with a detection limit of ~10 pM (Figure 3). This MPC SiNW-FET was applied to monitor the dopamine release under hypoxic stimulation from living PC12 cells. We resolved the controversial pathways that the increase in intracellular Ca²⁺ to trigger dopamine secretion is dominated by an extracellular Ca²⁺ influx, rather than the release of intracellular Ca²⁺ stores.

In conclusion, SiNW-FET biosensors have been successfully applied in biological and cellular studies, including the label-free and real-time recordings of neurotransmitter release, protein-protein interaction, virus detection, dopamine release from stimulated excitable cells, and clinical diagnosis. Finally, this novel bio-nano-electronic FET device, which is capable of integrating with living cell systems, provides a promising tool for biological analysis and cellular investigation and adds a new item to the biosensor toolbox for the future studies of cell biology and clinical disease diagnosis.

This work is partially supported by the Ministry of Science and Technology of Taiwan under NSC 101-2113-M-002-016-MY2 and NSC 102-2627-M-002-001.

Figure 1. Taking advantage of the reversible association-dissociation between glutathione (GSH) and glutathione S-transferase (GST), we built a reusable SiNW-FET biosensor for fast screening protein-protein interactions. The strategy used in the study includes the association of GST-tagged calmodulin (represented by CaM-GST) with a GSH-modified SiNW-FET (referred to as GSH/SiNW-FET) to form CaM/SiNW-FET, the subsequent detection of interacting proteins with CaM, and the removal of bound proteins via the dissociation of GSH-GST with concentrated GSH (³1 mM) washing solution. (PNAS, 107, 1047 (2010))

Figure 2. (a) An illustration for the detection of membrane fractions containing N-type voltage-gated Ca²⁺ channels (VGCCs) utilizing a CaM/SiNW-FET. (b–c) Real-time electrical detections of the binding of N-type VGCCs to the CaM/SiNW-FET in 0.1× PS (phosphate solution, consisting of 0.76 mM Na₂HPO₄ and 0.24 mM NaH₂PO₄ at pH 7.4) supplemented with (b) 100 mM Ca²⁺; (c) 500 mM EDTA. (d) Two control tests were conducted separately. (top graph) Electrical detection of the membrane fraction without the a1b subunit by CaM/SiNW-FET in 0.1× PS supplemented with 100 mM Ca²⁺. (bottom graph) Electrical detection of N-type VGCCs by GST/SiNW-FET (without CaM) in 0.1× PS supplemented with 100 mM Ca²⁺. (PNAS, 107, 1047 (2010))

Figure 3. (a) Schematics illustrate (top graph) the experimental setup of a DNA-aptamer/MPC SiNW-FET for detecting dopamine exocytosis from living PC12 cells under hypoxic stimulation and (bottom graph) the procedure for immobilization of the DNA-aptamer on the surface of SiNW. (b) An illustration about how the hypoxic condition triggers the dopamine (DA) exocytosis by the escalation of intracellular Ca²⁺ concentration via the hypothetical pathway of either extracellular Ca²⁺ influx (solid line) or intracellular Ca²⁺ store release (dashed line). (c) Real-time recordings for the dopamine exocytosis from living PC12 cells under different hypoxic stimulations: (upper trace) 35% [O₂] reduced buffer, (middle trace) 70% [O₂] reduced buffer, and (bottom trace) 70% [O₂] reduced buffer containing 1 mM CdI₂. (JACS, 135, 16034 (2013))