Surface Modification of Silicon Nanowire Based Field Effect Transistors with Stimuli Responsive Polymer Brushes for Biosensing Applications

Abstract

We demonstrate the functionalization of silicon nanowire based field effect transistors (SiNW FETs) FETs with stimuli-responsive polymer brushes of poly(N-isopropylacrylamide) (PNIPAAM) and poly(acrylic acid) (PAA). Surface functionalization was confirmed by atomic force microscopy, contact angle measurements, and verified electrically using a silicon nanowire based field effect transistor sensor device. For thermo-responsive PNIPAAM, the physicochemical properties (i.e., a reversible phase transition, wettability) were induced by crossing the lower critical solution temperature (LCST) of about 32 °C. Taking advantage of this property, osteosarcomic SaoS-2 cells were cultured on PNIPAAM-modified sensors at temperatures above the LCST, and completely detached by simply cooling. Next, the weak polyelectrolyte PAA, that is sensitive towards alteration of pH and ionic strength, was used to cover the silicon nanowire based device. Here, the increase of pH will cause deprotonation of the present carboxylic (COOH) groups along the chains into negatively charged COO− moieties that repel each other and cause swelling of the polymer. Our experimental results suggest that this functionalization enhances the pH sensitivity of the SiNW FETs. Specific receptor (bio-)molecules can be added to the polymer brushes by simple click chemistry so that functionality of the brush layer can be tuned optionally. We demonstrate at the proof-of concept-level that osteosarcomic Saos-2 cells can adhere to PNIPAAM-modified FETs, and cell signals could be recorded electrically. This study presents an applicable route for the modification of highly sensitive, versatile FETs that can be applied for detection of a variety of biological analytes.

Functional Devices from Bottom-Up Silicon Nanowires: A Review

“…At the same time, although silicon nanowires are considered promising for future biomedical sensors, their limited stability under physiological conditions is a challenge for sensor development. Solving this issue by surface engineering as described above opens up new possibilities for sensor improvements [ 81 , 196 , 197 ].…”

Responsive Polymer Brush Design and Emerging Applications for Nanotheranostics

“…In another similar example, PNIPAAm brushes were functionalized on silicon nanowire‐based field effect transistors (SiNW FETs) for the detection of human osteosarcomic Saos‐2 cells. [ 143 ] PNIPAAm brushes encountered reversible conformational changes in exposure to cell‐mediated external stimuli and monitored via the FET response. The use of this mixed polymer brush system could open up possibilities for designing highly reversible and tuneable biosensing systems for the detection of a variety of biological analytes including tumor cells.…”

Device Based on Polymer Schottky Junctions and Their Applications: A Review

“…The sensor can tolerate humidity from 20% to 80% and temperature from 10 ℃ to 40 ℃, making it suitable for practical agricultural applications. In addition to the gas sensor, the polymer-based Schottky junction devices can also seek promising applications in other types of chemical sensors or biosensors because of its chemical stability and simple polymerization approach [178], [179]. These sensors are envisioned to have tremendous potentials in the industrial environmental monitoring that detects hazardous substances, and wearable, portable health assessment devices that targets metabolites related to human health status [180].…”