The widespread and increasing interest in enhancing biosensing technologies by increasing their sensitivities and lowering their costs has led to the exploration and application of complex nanomaterials as signal transducers and enhancers. In this work, the electrochemical properties of monodispersed AuAg alloy nanoshells (NSs) with finely tunable morphology, composition, and size are studied to assess their potential as electroactive labels. The controlled corrosion of their silver content, caused by the oxidizing character of dissolved oxygen and chlorides of the electrolyte, allows the generation of a reproducible electrochemical signal that is easily measurable through voltammetric techniques. Remarkably, the underpotential deposition of dissolved Ag⁺ catalyzed on AuAg NS surfaces is observed and its dependence on the nanoparticle morphology, size, and elemental composition is studied, revealing a strong correlation between the relative amounts of the two metals. The highest catalytic activity is found at Au/Ag ratios higher than ≈ 10, showing how the synergy between both metals is necessary to trigger the enhancement of Ag⁺ reduction. The ability of AuAg NSs to generate an electrocatalytic current without the need for any strong acid makes them an extremely promising material for biosensing applications.

Environmental pollution is threatening human health and ecosystems as a result of modern agricultural techniques and industrial progress. A simple nanopaper-based platform coupled with luminescent bacteria Aliivibrio fischeri (A. fischeri) as a bio-indicator is presented here, for rapid and sensitive evaluation of contaminant toxicity. When exposed to toxicants, the luminescence inhibition of A. fischeri-decorated bioluminescent nanopaper (BLN) can be quantified and analyzed to classify the toxicity level of a pollutant. The BLN composite was characterized in terms of morphology and functionality. Given the outstanding biocompatibility of nanocellulose for bacterial proliferation, BLN achieved high sensitivity with a low cost and simplified procedure compared to conventional instruments for laboratory use only. The broad applicability of BLN devices to environmental samples was studied in spiked real matrices (lake and sea water), and their potential for direct and in situ toxicity screening was demonstrated. The BLN architecture not only survives but also maintains its function during freezing and recycling processes, endowing the BLN system with competitive advantages as a deliverable, ready-to-use device for large-scale manufacturing. The novel luminescent bacteria-immobilized, nanocelullose-based device shows outstanding abilities for toxicity bioassays of hazardous compounds, bringing new possibilities for cheap and efficient environmental monitoring of potential contamination.

A novel, miniaturized microfluidic platform was developed for the simultaneous detection and removal of polybrominated diphenyl ethers (PBDEs). The platform consists of a polydimethylsiloxane (PDMS) microfluidic chip for an immunoreaction step, a PDMS chip with an integrated screen-printed electrode (SPCE) for detection, and a PDMS-reduced graphene oxide (rGO) chip for physical adsorption and subsequent removal of PBDE residues. The detection was based on competitive immunoassay-linked binding between PBDE and PBDE modified with horseradish peroxidase (HRP-PBDE) followed by the monitoring of enzymatic oxidation of o-aminophenol (o-AP) using square wave anodic stripping voltammetry (SW-ASV). PBDE was detected with good sensitivity and a limit of detection similar to that obtained with a commercial colorimetric test (0.018 ppb), but with the advantage of using lower reagent volumes and a reduced analysis time. The use of microfluidic chips also provides improved linearity and a better reproducibility in comparison to those obtained with batch-based measurements using screen-printed electrodes. In order to design a detection system suitable for toxic compounds such as PBDEs, a reduced graphene oxide–PDMS composite was developed and optimized to obtain increased adsorption (based on both the hydrophobicity and π–π stacking between rGO and PBDE molecules) compared to those of non-modified PDMS. To the best of our knowledge, this is the first demonstration of electrochemical detection of flame retardants and a novel application of the rGO-PDMS composite in a biosensing system. This system can be easily applied to detect any analyte using the appropriate immunoassay and it supports operation in complex matrices such as seawater.