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

Stephanie Klinghammer,Sebastian Pregl,Gianaurelio Cuniberti,Sebastian Rauch,Petra Uhlmann,Larysa Baraban

doi:10.3390/mi11030274

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.

Highlights

There is an unceasingly high demand to develop novel biosensor platforms due to their wide range of potential applications in the fields of biotechnology, medicine, chemical analysis, and environmental monitoring [1]
In this study we investigated the effect of two stimuli-responsive polymer brushes towards the performance of bottom-up grown Silicon nanowires (SiNWs)-based field effect transistors (FETs) with Schottky junctions
The undoped silicon nanowires were grown via chemical vapor deposition (CVD) using gold NP seeds and subsequently aligned on the sensor substrate to achieve a parallel array of nanowires [59,60]

Summary

Introduction

There is an unceasingly high demand to develop novel biosensor platforms due to their wide range of potential applications in the fields of biotechnology, medicine, chemical analysis, and environmental monitoring [1]. Electrochemical sensors are capable of transforming biological signals into electric ones while operating rapidly, with low detection limits, and are easy to integrate into microelectronic circuits [2,3,4,5,6]. Field effect transistor devices can play a key role in the aforementioned applications (e.g., biosensing), as the majority of biomolecules and bioreactions involve charge and potential shifts that can be detected electrically [7,8,9]. Among other systems [15,16,17], silicon nanowire structured field effect transistors (FETs) are suitable for detecting of a wide variety of biological entities (i.e., DNA, nucleic acids, proteins, viruses, and cells), each with supreme limit of detection [18,19,20,21,22,23,24]

Methods

Results

Conclusion