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The use of enzyme-based biosensors for the detection and quantification of analytes of interest such as contaminants of emerging concern, including over-the-counter medication, provides an attractive alternative compared to more established techniques. However, their direct application to real environmental matrices is still under investigation due to the various drawbacks in their implementation. Here, we report the development of bioelectrodes using laccase enzymes immobilized onto carbon paper electrodes modified with nanostructured molybdenum disulfide (MoS2). The laccase enzymes were two isoforms (LacI and LacII) produced and purified from the fungus Pycnoporus sanguineus CS43 that is native to Mexico. A commercial purified enzyme from the fungus Trametes versicolor (TvL) was also evaluated to compare their performance. The developed bioelectrodes were used in the biosensing of acetaminophen, a drug widely used to relieve fever and pain, and of which there is recent concern about its effect on the environment after its final disposal. The use of MoS2 as a transducer modifier was evaluated, and it was found that the best detection was achieved using a concentration of 1 mg/mL. Moreover, it was found that the laccase with the best biosensing efficiency was LacII, which achieved an LOD of 0.2 µM and a sensitivity of 0.108 µA/µM cm2 in the buffer matrix. Moreover, the performance of the bioelectrodes in a composite groundwater sample from Northeast Mexico was analyzed, achieving an LOD of 0.5 µM and a sensitivity of 0.015 µA/µM cm2. The LOD values found are among the lowest reported for biosensors based on the use of oxidoreductase enzymes, while the sensitivity is the highest currently reported. [ABSTRACT FROM AUTHOR]

A Surface Plasmon Resonance (SPR) biosensor based on an inhibition immunoassay was developed for the detection of diclofenac (DCF) in aqueous solution. Due to the small size of DCF, an hapten-protein conjugate was produced by coupling DCF to bovine serum albumin (BSA). DCF-BSA conjugate formation was confirmed via MALDI-TOF mass spectrometry. The resulting conjugate was immobilized onto the surface of a sensor fabricated via e-beam deposition of a 2 nm chromium adhesion layer followed by a 50 nm gold layer onto precleaned BK7 glass slides. Immobilization onto the nano thin gold surface was accomplished by covalent amide linkage through a self-assembled monolayer. Samples were composed of a mixture of antibody at a fixed concentration and DCF at different known concentrations in deionized water, causing the inhibition of anti -DCF on the sensor. The DCF-BSA was obtained with a ratio of 3 DCF molecules per BSA. A calibration curve was performed using concentrations between 2 and 32 μg L−1. The curve was fitted using the Boltzmann equation, reaching a limit of detection (LOD) of 3.15 μg L−1 and limit of quantification (LOQ) of 10.52 μg L−1, the inter-day precision was calculated and an RSD value of 1.96% was obtained; and analysis time of 10 min. The developed biosensor is a preliminary approach to the detection of DCF in environmental water samples, and the first SPR biosensor developed for DCF detection using a hapten-protein conjugate. [Display omitted] • An SPR immunosensor was developed to detect diclofenac in water samples. • The configuration of the immunosensor involves the conjugation of diclofenac and BSA as a carrier protein. • This is the first SPR immunosensor for diclofenac that uses the target analyte conjugated to a protein. • The obtained results are comparable with the only other work published for diclofenac detection using SPR. • The development of this kind of biosensors could help to star regulating the discharge of diclofenac in water. [ABSTRACT FROM AUTHOR]

• A novel methodology using an effective refractive index to characterize the surface plasmon resonance angle. • Optical technique for detection of bovine serum albumin and carbamazepine • Possibility to infer changes onto the surface of gold films using microfluidic systems. Surface plasmon resonance was used for the detection of different kinds of organic molecules, which was achieved employing a Kretschmann configuration. A simple theoretical model based on effective medium theory was used for estimation of the SPR angle. The employed model considers an effective refractive index, which has some advantages in comparison to other effective medium theories. This model depends on the surface coverage, size of the sample and also considers the scattering by molecules deposited on the surface of the thin film. Using an effective refractive index as a tool to predict the behavior of the SPR signal offers a significant advantage for the development of new biosensors, providing a deeper physical insight on the behavior of such phenomena, since inferring the behavior of SPR signals is of great importance for chemical analysis and bio-sensing. Therefore, in this work, an effective medium model was compared with experimental SPR measurements as a function of angle incidence of different molecules deposited onto thin films, specifically Bovine Serum Albumin (BSA) and carbamazepine attached to BSA, in order to validate the theoretical model. Evaluation of the proposed model for SPR signal was in good agreement with the experimental results. Statistical tests were obtained, with a 99% of correlation between the experimental data and the theoretical predictions around the resonance. [ABSTRACT FROM AUTHOR]