Whole virus detection using aptamers and paper-based sensor potentiometry.

Paper-based sensors, microfluidic platforms and electronics have attracted attention in the past couple of decades because they are flexible, can be recycled easily, environmentally friendly and inexpensive. Here, we report a paper-based potentiometric sensor to detect the whole Zika virus with a minimum sensitivity of 0.26 nV/Zika and a minimum detectable signal (MDS) of 2.4x107 Zika. Our paper sensor works very similar to a P-N junction where a junction is formed between two different regions with different electrochemical potentials on the paper. These two regions with slightly different ionic contents, ionic species and concentrations, produce a potential difference given by the Nernst equation. Our paper sensor consists of 2-3 × 10 mm segments of paper with conducting silver paint contact patches on two ends. The paper is dipped in a buffer solution containing aptamers designed to bind to the capsid proteins on Zika. We then added the Zika (in its own buffer) to the region close to one of the silver paint contacts. The Zika virus (40 nm diameter with 43 kDa or 7.1 × 10-20 gm weight) became immobilized in the paper's pores and bonded with the resident aptamers creating a concentration gradient. Atomic force microscopy and Raman spectroscopy were carried out to verify that both the aptamer and Zika become immobilized in the paper. The potential measured between the two silver paint contacts reproducibly became more negative upon adding the Zika. We also showed that a liquid crystalline display (LCD) powered by the sensor can be used to read the sensor output.

Bio-mimetic synthetic cell hydrogel magnetometer.

We present a bio-inspired hydrogel magnetometer where the cell potential (V oc) between two hydrogels is used to measure an external magnetic field. Ferromagnetic particles located in the hydrogels move in response to the external field and change the V oc (sensitivity ~ 3.7 V T-1). As the field becomes larger than a critical field B c (~38 mT), these particles puncture the hydrogel boundary shorting out the concentration gradient region and abruptly reducing the V oc (sensitivity ~ 23.5 V T-1). In this regime, the V oc behaves similar to the neuron firing. In subsequent measurement cycles, the particles remain in punctured holes and the sensor behaviour is neuron-like with lower sensitivity (~20 V T-1). V oc also changes as a function of pressure (8 mV kPa-1) and temperature (2 mV K-1). After 4 h, the ionic concentration gradient diminishes in the device, and similar to biological cell fatigue, V oc decreases and can be recharged with many different techniques.

Remote Microwave and Field-Effect Sensing Techniques for Monitoring Hydrogel Sensor Response.

This paper presents two novel techniques for monitoring the response of smart hydrogels composed of synthetic organic materials that can be engineered to respond (swell or shrink, change conductivity and optical properties) to specific chemicals, biomolecules or external stimuli. The first technique uses microwaves both in contact and remote monitoring of the hydrogel as it responds to chemicals. This method is of great interest because it can be used to non-invasively monitor the response of subcutaneously implanted hydrogels to blood chemicals such as oxygen and glucose. The second technique uses a metal-oxide-hydrogel field-effect transistor (MOHFET) and its associated current-voltage characteristics to monitor the hydrogel's response to different chemicals. MOHFET can be easily integrated with on-board telemetry electronics for applications in implantable biosensors or it can be used as a transistor in an oscillator circuit where the oscillation frequency of the circuit depends on the analyte concentration.