Infections caused by various known and emerging pathogenic microorganisms, including antibiotic-resistant strains, are a major threat to global health and well-being. This highlights the urgent need for detection systems for microbial identification, quantification and characterization towards assessing infections, prescribing therapies and understanding the dynamic cellular modifications. Current state-of-the-art microbial detection systems exhibit a trade-off between sensitivity and assay time, which could be alleviated by selective and label-free microbial capture onto the sensor surface from dilute samples. AC electrokinetic methods, such as dielectrophoresis, enable frequency-selective capture of viable microbial cells and spores due to polarization based on their distinguishing size, shape and sub-cellular compositional characteristics, for downstream coupling to various detection modalities. Following elucidation of the polarization mechanisms that distinguish bacterial cells from each other, as well as from mammalian cells, this review compares the microfluidic platforms for dielectrophoretic manipulation of microbials and their coupling to various detection modalities, including immuno-capture, impedance measurement, Raman spectroscopy and nucleic acid amplification methods, as well as for phenotypic assessment of microbial viability and antibiotic susceptibility. Based on the urgent need within point-of-care diagnostics towards reducing assay times and enhancing capture of the target organism, as well as the emerging interest in isolating intact microbials based on their phenotype and subcellular features, we envision widespread adoption of these label-free and selective electrokinetic techniques.

No abstract

We report a disposable point-of-care sensing platform specific to salivary cortisol detection. The sensor is inkjet printed on a paper substrate with a metalloporphyrin based macrocyclic catalyst ink that can electrochemically reduce cortisol, captured by aptamer functionalized magnetic nanoparticles. The sensor consists of a thin magnet disc, aligned at the back of the electrode, in order to populate the magnetic nanoparticle bound cortisol at the sensing electrode area. Proof of concept studies were performed to detect salivary cortisol levels in human subjects with high and low risks for obstructive sleep apnea (OSA). High selectivity was observed to salivary cortisol against a background of closely related steroids.

No abstract

We report the design and characterization of a disposable light shielded paper-plastic microfluidic device that can detect nanomolar levels of H2O2 using a smartphone camera and a light sealed accessory. Chemiluminescence reaction of H2O2 with bis(2,4,6-trichlorophenyl)oxalate in the presence of rubrene and imidazole is confined to a paper reaction site where the individual reagents are delivered via plastic microfluidic channels. The net photon emission from the chemiluminescence reactions, detected by using a smartphone, is correlated with H2O2 concentrations. With a total reagent volume of 25 μL, the sensor system was able to detect H2O2 concentrations as low as 250 nM. The smartphone based chemiluminescence sensing system has great potential as a point of care diagnostic tool for monitoring nanomolar levels of H2O2 in biological samples.

We introduce a flexible microfluidic bioimpedance sensor that is capable of detecting biomass and cell viability variations in a cell suspension. The sensor is developed on indium tin oxide (ITO) coated polyethylene terephthalate (PET) substrate and is devoid of gold, silicon, PDMS, or glass. In conjugation with a custom built PCB read-out module, the impedance characteristics of a cell suspension can be measured within one minute of sample introduction using liquid volumes less than 5 μL. The portable sensor system occupies very little bench space and has the potential to be developed as a disposable electrical bioimpedance probe for rapid detection of dielectric variations in a biological suspension. The sensor is designed to generate a differential impedance spectra exclusive to a cell suspension with a dual-electrode-pair system. The potential of the sensor to discriminate between live and heat treated Saccharomyces cerevisiae is demonstrated in this study. The disposable sensor along with the distance variation technique is touted to be an inexpensive alternative to some of the existing online disposable biomass detection probes and electrochemical sensors.

We report dielectrophoretic (DEP) assembly of biological cells and microparticles using platinum-black electrodeposited conductive textile fiber. The threedimensional conductive structures with high aspect ratios were found to facilitate high electric field regions, as revealed by scanning electron microscope characterization. The effective conducting area (A eff ) and its stability of thread electrodes were estimated using electrochemical methods. Potential of platinum black electrodeposited thread as 3-D electrodes for creating high gradient electrical field for dielectrophoretic assembly of microspheres and Saccharomyces cerevisiae (yeast cells) into 1D and two-dimensional structures over long ranges under the application of low voltages (4-10 V pp ) has been demonstrated. The formation of highly ordered pearl chains of microparticles using thread electrodes when subjected to dielectrophoresis (DEP) has been discussed in detail. Published by AIP Publishing.

There is considerable interest in nanostructured materials with interdigitated electrodes (IDEs) platforms to detect and monitor the level of various ions in numerous applications. Herein, we report the design and fabrication of IDEs based pH sensor by using hydrothermal growth of ZnO nanorods (NRs). A four-step deposition of ZnO seed layer followed by a hydrothermal treatment lead to the heavily ordered ZnO NRs patterns on the screen printed IDEs. The structural, chemical compositional and electrical properties of the NRs were investigated and examined by using field emission scanning electron microscopy (FeSEM), atomic force microscopy (AFM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) technique and Keithley 4200 semiconductor characterization system respectively. The sensor capacitance and pH were found to be inversely proportional at a working frequency of 1 kHz. The sensor displayed sensitivity of 1.06 nF/pH in the range of pH 4−10.