Although there exist numerous established laboratory-based technologies for sample diagnostics and analyte detection, many medical and forensic science applications require point of care based platforms for rapid on-the-spot sample analysis. Electrochemical biosensors provide a promising avenue for such applications due to the portability and functional simplicity of the technology. However, the ability to develop such platforms with the high sensitivity and selectivity required for analysis of low analyte concentrations in complex biological samples remains a paramount issue in the field of biosensing. Nonspecific adsorption, or fouling, at the electrode interface via the innumerable biomolecules present in these sample types (i.e., serum, urine, blood/plasma, and saliva) can drastically obstruct electrochemical performance, increasing background "noise" and diminishing both the electrochemical signal magnitude and specificity of the biosensor. Consequently, this review aims to discuss strategies and concepts used throughout the literature to prevent electrode surface fouling in biosensors and to communicate the nature of the antifouling mechanisms by which they operate. Evaluation of each antifouling strategy is focused primarily on the fabrication method, experimental technique, sample composition, and electrochemical performance of each technology highlighting the overall feasibility of the platform for point of care based diagnostic/detection applications.

Cyanobacteria have a wide range of impact on natural ecosystems, and have been recognized as potentially rich sources of pharmacological and structurally interesting secondary metabolites. To better understand the basic molecular processes and mechanisms that influence and regulate the growth (like length) of cyanobacteria, or connections between environment, genotype, and phenotype, it would be essential to separate shapesynchronized cyanobacterial cell populations with relatively uniform length and size. This work proposes a novel and efficient method to separate cyanobacterial Anabaena by shape (rod aspect ratio) using viscoelastic microfluidics in a straight channel with expansion−contraction cavity arrays (ECCA channel). The biocompatible viscoelastic solutions with dissolved polymer would induce a combined effect of inertial lift force, elastic force, and secondary drag force for Anabaena flowing in it. Therefore, Anabaena with different lengths reach different lateral equilibrium positions and flow out from different outlets. Factors including flow rate, fluid viscoelasticity, channel structure, and length on the shape-based cell separation were studied systematically. This work, for the first time, demonstrates continuous and sheathless shapebased separation of cyanobacteria using viscoelastic microfluidics. Moreover, its ability to manipulate objects with different morphologies and with a size of >100 μm will extend the capability of microfluidics to a completely new field that has never been reached and would be attractive across a range of new applications.

We examined a series of commercially available screen-printed electrodes (SPEs) for their suitability for electrochemical and electrogenerated chemiluminescence (ECL) detection systems. Using cyclic voltammetry with both a homogeneous solution-based and a heterogeneous bead-based ECL assay format, the most intense ECL signals were observed from unmodified carbon-based SPEs. Three commercially available varieties were tested, with Zensor outperforming DropSens and Kanichi in terms of sensitivity. The incorporation of nanomaterials in the electrode did not significantly enhance the ECL intensity under the conditions used in this evaluation (such as gold nanoparticles 19%, carbon nanotubes 45%, carbon nanofibers 21%, graphene 48%, and ordered mesoporous carbon 21% compared to the ECL intensity of unmodified Zensor carbon electrode). Platinum and gold SPEs exhibited poor relative ECL intensities (16% and 10%) when compared to carbonaceous materials, due to their high rates of surface oxide formation and inefficient oxidation of tri-n-propylamine (TPrA). However, the ECL signal at platinum electrodes can be increased ∼3-fold with the addition of a surfactant, which enhanced TPrA oxidation due to increasing the hydrophobicity of the electrode surface. Our results also demonstrate that each SPE should only be used once, as we observed a significant change in ECL intensity over repeated CV scans and SPEs cannot be mechanically polished to refresh the electrode surface.

Noble-metal nanoparticles (NMNPs) have unique properties beneficial for the development of novel reporting technologies to enhance the detection sensitivity and specificity of clinically validated biomarkers. Unique size-and shape-dependent optical, catalytic, and magnetic properties of NMNPs have enabled significant advances in biosensing due to facilitation of colorimetric detection, localized surface plasmon resonance, fluorescence enhancement/quenching, surface-enhanced Raman scattering, electrochemical activity, etc. Among these, the colorimetric detection method is highly attractive for use in point-of-need diagnostic applications in which color changes in the presence of biomarkers can be directly observed with the naked eye without the requirement of any equipment. This capability fulfills one of the main requirements set by the World Health Organization to provide people living in remote/regional/low-resource settings access to effective and comprehensive primary care. Although there are many scientific publications, the commercialization of NMNP-based colorimetric diagnostic assays for point-of-need applications is lagging mainly because of the lack of knowledge related to NMNPs in dealing with biological samples and sensitivity of the tests required for the real-world applications. Herein, we provide a critical review of the fundamentals of NMNPs and the recent progress in their usage for monitoring and detecting clinically relevant biomarkers in biological samples at the point-of-need to scientifically assess the benefits and limitations of this technology. We then compare the methods employed to enhance the sensitivity of colorimetric assays in detecting clinically validated target biomarkers in body fluids. Finally, we investigate the future trends and strategies that deserve more research to increase the successful commercialization of these assays.

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