Label free detection of miRNA-21 with electrolyte gated organic field effect transistors (EGOFETs).

We report a dual gate/common channel organic transistor architecture designed for quantifying the concentration of one of the strands of miRNA-21 in solution. The device allows one to measure the differential response between two gate electrodes, viz. one sensing and one reference, both immersed in the electrolyte above the transistor channel. Hybridization with oligonucleotide in the picomolar regime induces a sizable reduction of the current flowing through the transistor channel. The device signal is reported at various gate voltages, showing maximum sensitivity in the sublinear regime, with a limit of detection as low as 35 pM. We describe the dose curves with an analytical function derived from a thermodynamic model of the reaction equilibria relevant in our experiment and device configuration, and we show that the apparent Hill dependence on analyte concentration, whose exponent lies between 0.5 and 1, emerges from the interplay of the different equilibria. The binding free energy characteristic of the hybridization on the device surface is found to be approximately 20% lower with respect to the reaction in solution, hinting to partially inhibiting effect of the surface and presence of competing reactions. Impedance spectroscopy and surface plasmon resonance (SPR) performed on the same oligonucleotide pair were correlated to the electronic current transduced by the EGOFET, and confirmed the selectivity of the biorecognition probe covalently bound on the gold surface.

Label-free immunodetection of α-synuclein by using a microfluidics coplanar electrolyte-gated organic field-effect transistor.

The aggregation of α-synuclein is a critical event in the pathogenesis of neurological diseases, such as Parkinson or Alzheimer. Here, we present a label-free sensor based on an Electrolyte-Gated Organic Field-Effect Transistor (EGOFET) integrated with microfluidics that allows for the detection of amounts of α-synuclein in the range from 0.25 pM to 25 nM. The lower limit of detection (LOD) measures the potential of our integrated device as a tool for prognostics and diagnostics. In our device, the gate electrode is the effective sensing element as it is functionalised with anti-(α-synuclein) antibodies using a dual strategy: i) an amino-terminated self-assembled monolayer activated by glutaraldehyde, and ii) the His-tagged recombinant protein G. In both approaches, comparable sensitivity values were achieved, featuring very low LOD values at the sub-pM level. The microfluidics engineering is central to achieve a controlled functionalisation of the gate electrode and avoid contamination or physisorption on the organic semiconductor. The demonstrated sensing architecture, being a disposable stand-alone chip, can be operated as a point-of-care test, but also it might represent a promising label-free tool to explore in-vitro protein aggregation that takes place during the progression of neurodegenerative illnesses.