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Nanostructured microelectrodes (NMEs) are an attractive alternative to yield sensitive bioassays in unprocessed samples. However, although valuable for different applications, nanoporous NMEs usually cannot boost the sensitivity of diffusion-limited analyses because of the enlarged Debye length within the nanopores, which reduces their accessibility. To circumvent this limitation, nanopore-free gold NMEs were electrodeposited from 45 μm SU-8 apertures, featuring nanoridged microspikes on a recessed surface of gold thin film while carrying interconnected crown-like and spiky structures along the edge of a SU-8 passivation layer. These structures were grown onto ultradense, vertical array chips that offer a promising strategy for translating reproducible, high-resolution, and cost-effective sensors into real-world applications. The NMEs yielded reproducible analyses, while machine learning allowed us to predict the analytical responses from NME electrodeposition data. By taking advantage of the high surface area and accessible structure of the NMEs, these structures provided a sensitivity for [Fe(CN) 6 ] 3-/4- that was 5.5× higher than that of bare WEs while also delivering a moderate antibiofouling property in undiluted human plasma. As a proof of concept, these electrodes were applied toward the fast (22 min) and simple determination of Staphylococcus aureus by monitoring the oxidation of [Fe(CN) 6 ] 4- , which acted as a cellular respiration rate redox reporter. The sensors also showed a wide dynamic range, spanning 5 orders of magnitude, and a calculated limit of detection of 0.2 CFU mL -1 .

Low-cost, instrument-free colorimetric tests were developed to detect SARS-CoV-2 using plasmonic biosensors with Au nanoparticles functionalized with polyclonal antibodies (f-AuNPs). Intense color changes were noted with the naked eye owing to plasmon coupling when f-AuNPs form clusters on the virus, with high sensitivity and a detection limit of 0.28 PFU mL -1 (PFU stands for plaque-forming units) in human saliva. Plasmon coupling was corroborated with computer simulations using the finite-difference time-domain (FDTD) method. The strategies based on preparing plasmonic biosensors with f-AuNPs are robust to permit SARS-CoV-2 detection via dynamic light scattering and UV-vis spectroscopy without interference from other viruses, such as influenza and dengue viruses. The diagnosis was made with a smartphone app after processing the images collected from the smartphone camera, measuring the concentration of SARS-CoV-2. Both image processing and machine learning algorithms were found to provide COVID-19 diagnosis with 100% accuracy for saliva samples. In subsidiary experiments, we observed that the biosensor could be used to detect the virus in river waters without pretreatment. With fast responses and requiring small sample amounts (only 20 μL), these colorimetric tests can be deployed in any location within the point-of-care diagnosis paradigm for epidemiological control.

The investigation of enhanced Raman signal effects and the preparation of high-quality, reliable surface-enhanced Raman scattering (SERS) substrates is still a hot topic in the SERS field. Herein, we report an effect based on the shape-induced enhanced Raman scattering (SIERS) to improve the action of gold nanorods (AuNRs) as a SERS substrate. Scattered electric field simulations reveal that bare V-shaped Si substrates exhibit spatially distributed interference patterns from the incident radiation used in the Raman experiment, resulting in constructive interference for an enhanced Raman signal. Experimental data show a 4.29 increase in Raman signal intensity for bare V-shaped Si microchannels when compared with flat Si substrates. The combination of V-shaped microchannels and uniform aggregates of AuNRs is the key feature to achieve detections in ultra-low concentrations, enabling reproducible SERS substrates having high performance and sensitivity. Besides SIERS effects, the geometric design of V-shaped microchannels also enables a "trap" to the molecule confinement and builds up an excellent electromagnetic field distribution by AuNR aggregates. The statistical projection of SERS spectra combined with the SIERS effect displayed a silhouette coefficient of 0.83, indicating attomolar (10 -18 mol L -1 ) detection with the V-shaped Si microchannel.

The fast growth of celiac disease diagnosis has sparked the production of gluten-free food and the search for reliable methods to detect gluten in foodstuff. In this paper, we report on a microfluidic electronic tongue (e-tongue) capable of detecting trace amounts of gliadin, a protein of gluten, down to 0.005 mg kg -1 in ethanol solutions, and distinguishing between gluten-free and gluten-containing foodstuff. In some cases, it is even possible to determine whether gluten-free foodstuff has been contaminated with gliadin. That was made possible with an e-tongue comprising four sensing units, three of which made of layer-by-layer (LbL) films of semiconducting polymers deposited onto gold interdigitated electrodes placed inside microchannels. Impedance spectroscopy was employed as the principle of detection, and the electrical capacitance data collected with the e-tongue were treated with information visualization techniques with feature selection for optimizing performance. The sensing units are disposable to avoid cross-contamination as gliadin adsorbs irreversibly onto the LbL films according to polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) analysis. Small amounts of material are required to produce the nanostructured films, however, and the e-tongue methodology is promising for low-cost, reliable detection of gliadin and other gluten constituents in foodstuff.

The need for analytical devices for detecting cancer at early stages has motivated research into nanomaterials where synergy is sought to achieve high sensitivity and selectivity in low-cost biosensors. In this study, we developed a film architecture combining self-assembled monolayer (SAM) and layer-by-layer (LbL) films of polysaccharide chitosan and the protein concanavalin A, on which a layer of anti-CA19-9 antibody was adsorbed. Using impedance spectroscopy with this biosensor, we were capable of detecting low concentrations of the antigen CA19-9, an important biomarker for pancreatic cancer. The limit of detection of 0.69U/mL reached is sufficient for detecting pancreatic cancer at very early stages. The selectivity of the biosensor was inferred from a series of control experiments with samples of cell lines that were tested positive (HT29) and negative (SW620) for the biomarker CA19-9, in addition to the lack of changes in the capacitance value for other analytes and antigen that are not related to this type of cancer. The high sensitivity and selectivity are ascribed to the very specific antigen-antibody interaction, which was confirmed with PM-IRRAS and atomic force microscopy. Also significant is that used information visualization methods to show that different cell lines and commercial samples containing distinct concentrations of CA19-9 and other analytes can be easily distinguished from each other. These computational methods are generic and may be used in optimization procedures to tailor biosensors for specific purposes, as we demonstrated here by comparing the performance of two film architectures in which the concentration of chitosan was varied.

The need for early detection of various diseases, including breast cancer, has motivated research into nanomaterials that can be assembled in organized films which serve as biosensors. Owing to the variety of possible materials and film architectures, procedures are required to design optimized biosensors. In this study, we combine surface-specific methods to monitor the assembly of antibodies on nanostructured films with two distinct architectures. In the first, a layer of the antibody type mouse anti-HER2 (clone tab250) was immobilized on a self-assembled monolayer (SAM) of 11-mercaptoundecanoic acid modified with N-hydroxysuccinimide (NHS) and 1-ethyl-3-(3-(dimethylamino)propyl)carbodiimide (EDC). In the second approach, a SAM of cysteamine was coated with a biotin/spreptavidin bilayer on which a layer of biotinylated antibody type MSx2HUp185/her biotin was adsorbed. The rougher, less passivating coating with cysteamine determined from cyclic voltammetry and scanning electron microscopy led to biosensors that are more sensitive to detect the breast cancer ERBB2 (HER2) biomarker in impedance spectroscopy measurements. This higher distinguishing ability of the cysteamine-containing film architecture was proven with information visualization methods to treat the impedance data. Polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) confirmed that biosensing resulted from the antibody-ERBB2 antigen affinity.