362158 Printed, Electrolyte-Gated Transistors As Label-Free DNA Sensors
PRINTED, ELECTROLYTE-GATED TRANSISTORS
AS LABEL-FREE BIOSENSORS
Scott P. White, Kevin D. Dorfman, C. Daniel Frisbie,
Department of Chemical Engineering and Materials Science
University of Minnesota, Minneapolis, MN 55455, USA
We have developed a sensor for electronic, label-free detection of bio-recognition events. An electrolyte-gated transistor (EGT) transduces the binding of biomolecules into an electronic signal when they are selectively immobilized to the sensor surface. A floating-gate electrode electronically connects the analyte containing solution to the EGT while keeping them physically separated from another. The fabrication method, ease of use, and compatibility with flexible substrates make this an easily multiplexed biosensor for field applications in forensics, biothreat detection, and pathogen screening.
The key component of the sensor is an EGT that utilizes the high capacitance of mobile ions to modulate the conductivity of an organic semiconductor under the application of low input voltages. The source of mobile ions is an ion-gel dielectric layer formed by gelating a block copolymer in an ionic liquid. Due to their solution processability, high ionic conductivity, and high capacitance, ion-gels have been successfully used as dielectric layers in organic electronic transistors, circuits, and displays, but this our lab’s first work to use them for biosensors . To facilitate interaction with biomolecules a planar, floating gate geometry is implemented to decouple the electronic materials from an aqueous solution containing analyte molecules for detection. Binding analytes to capture molecules tethered to the floating-gate/aqueous interface shifts the voltage through the EGT by altering the work function of the functionalized electrode.
Device fabrication begins with gold contacts photolithographically patterned on a silicon wafer. Next, the benchmark semiconducting polymer, poly(3-hexylthiophene) or P3HT, and the ion-gel are deposited from solution at low temperature (60C) using an aerosol-jet printing technique. The side-gated EGT is then interfaced with an aqueous electrolyte contained by an elastomeric well made from poly(dimethylsiloxane) or PDMS. Capture molecules are tethered to the floating-gate/aqueous electrolyte interface with a thiol/gold chemistry allowing for selective binding of analyte molecules to the electrode surface. As a proof of principle, we used thiol-modified ssDNA strands as capture molecules and complementary oligonucleotides as analytes.
The sensors are tested by sweeping the gate bias and measuring the current through the semiconductor generating a transfer curve. The crucial concept of this work is that the effective gate voltage controlling current through the semiconductor depends on the composition of a monolayer formed on the aqueous arm of the floating-gate electrode. This way, bio-recognition events leading to surface modification can be interpreted as shifting current-voltage relationships. The high transconductance of the EGT causes the relatively small changes in work function due to DNA hybridization (~0.1 eV) to produce large changes in current through the EGT. The device can be readily integrated with a microfluidic system in a large area array where many EGTs are functionalized and tested in parallel to characterize a biochemical mixture in a high-throughput, label-free manner.
- Kim, S. H. et al. Electrolyte-Gated Transistors for Organic and Printed Electronics. Adv. Mater. 25, 1822–1846 (2013).