Sensing of TNT with APTES modified Silicon nanowires

 

 Overview

Our work shows, for the first time, the use of silicon-nanowire “electrical–nose” arrays as an effective platform of unprecedented outstanding detection capability for TNT down to a detection limit of ~0.1 femtomolar (~1x10-6 ppt). This supersensitive, label-free, multiplexed, real-time and rapid electrical detection of TNT is achieved by the surface functionalization of SiNW devices with an electron-rich amino-silane (APTES) which binds the electron-deficient explosive molecules (e.g. TNT) through charge-transfer donor-acceptor interactions leading to charged TNT-amine complexes in close proximity to the nanowire surface, thus causing sharp changes in the conductance of the electrical-sensing nanoelements. This, in turn, results in an unprecedented detection sensitivity limit for TNT in aqueous solutions, as well as for TNT vapors sampled directly from the air. By virtue of the extraordinary sensitivity shown, our sensor platform seems not to be limited by the intrinsic low volatility of most explosive species and obviously has significant advantages over current detection strategies.

 

Sensing of TNT with APTES modified Silicon nanowires

 

The “Nano-sensors” can be used to detect TNT in solution as well as in the gas phase. The response time is very rapid and the sensor is reversible and can be regenerated quickly by a simple wash with a reference solution.) a) Normalized conductance-versus-time of an APTES functionalized p-type SiNW FET sensor following the alternate delivery of TNT solutions of different concentrations and a reference solution. (a-g) correspond to TNT concentrations of 500 fM, 5 pM, 5 nM, 75 nM, 100 nM, 500 nM, 5 mM.  (b) Relative percent conductance change (DG/G0) versus TNT concentration (drawn on a logarithmic scale). (c) Relative percent conductance change (DG/G0) versus TNT concentration for an exceptionally sensitive device. (d) Relative percent conductance change (DG/G0) recorded simultaneously from three APTES functionalized p-type SiNW FET upon exposure to a 5 mM TNT solution.

      

Experimental system

Sensing of TNT experimental

The TNT was dissolved in 0.1%DMSO in a DI H2O and was delivered to the chip by the microfluidic system by means of a syringe pump at a flow rate of 5μl/min. The conductance of the NWFET was measured by application of AC bias (70kHz, 30mV) by means of a lock-in amplifier and the drain current was amplified with a variable-gain amplifier and filtered by the lock-in amplifier.  The output data were recorded by using a multichannel  I/O adaptor panel.

 

Results

The “Nano-sensors” can be used to detect TNT in solution as well as in the gas phase. The response time is very rapid and the sensor is reversible and can be regenerated quickly by a simple wash with a washing solution.

Sensing of TNT results

[a]: Normalized conductance vs. time of APTES functionalized p-type SiNW FET sensor following the alternate delivery of TNT solutions of different concentrations. (points I-VII) correspond to TNT concentrations of 500 fM, 5 pM, 5 nM, 75 nM, 100 nM, 500 nM, 5 mM, respectively.  [b] Relative percent conductance change (DG/G0) versus TNT concentration (drawn on a logarithmic scale). [c] Relative percent conductance change (DG/G0) recorded simultaneously from three APTES functionalized p-type SiNW FET upon exposure to a 5 mM TNT solution.