Surface enhanced Raman spectroscopy (SERS) is becoming a paramount analytical mechanism in nanotechnology and biological/chemical detection. However, fabrication of highly sensitive SERS substrates often involves expensive and time‐consuming procedures and the resulting materials require careful handling. Herein, a simple‐to‐manufacture, highly sensitive, and easy‐to‐handle SERS substrate enabled by plasmonic nanopaper decorated with graphene oxide flakes is reported. Owing to the physicochemical properties gathered by this SERS substrate, the nanocomposite leads to a flexible platform facilitating: a) analysis of the model analyte (Rhodamine 6G) via a high energy laser (457 nm) with negligible fluorescent background, which is important to achieve the maximum excitation of the respective localized surface plasmon resonance; b) a charge transferring phenomenon associated to the graphene derivative that, operating in synergy with the previous phenomenon, enhances the SERS signal and allows an analytical limit of detection of 0.13 × 10−9 m, which is about 2900‐fold lower than that obtained with the counterpart substrate made of silver nanoparticle‐decorated nanopaper; c) an ultrastable signal which remains completely constant at least during 50 days. Furthermore, the resulting SERS substrate is amenable to a cost‐efficient and large‐scale production process, which furthers laboratory and real world applications of SERS.

The working area of a screen-printed electrode, SPE, was modified with the enzyme tyrosinase (Tyr) using different immobilization methods, namely entrapment with water-soluble polyvinyl alcohol (PVA), cross-linking using glutaraldehyde (GA), and cross-linking using GA and human serum albumin (HSA); the resulting electrodes were termed SPE/Tyr/PVA, SPE/Tyr/GA and SPE/Tyr/HSA/GA, respectively. These biosensors were characterized by means of amperometry and EIS techniques. From amperometric evaluations, the apparent Michaelis-Menten constant, Km′, of each biosensor was evaluated while the respective charge transfer resistance, Rct, was assessed from impedance measurements. It was found that the SPE/Tyr/GA had the smallest Km′ (57 ± 7) μM and Rct values. This electrode also displayed both the lowest detection and quantification limits for catechol quantification. Using the SPE/Tyr/GA, the Trolox Equivalent Antioxidant Capacity (TEAC) was determined from infusions prepared with “mirto” (Salvia microphylla), “hHierba dulce” (Lippia dulcis) and “salve real” (Lippia alba), medicinal plants commonly used in Mexico.

Potentiometric studies are presented here on solid contact ion-selective electrodes, based on neutral carriers comprising structural sulfur−donating groups and an aliphatic chain, where the latter confers stability to the molecule for the formation of metal complexes. As result, an ISE was obtained for the potentiometric determination of mercury. This sensor allowed continuous mercury determinations at nanomolar levels within a wide concentration interval (1.0 × 10 −9 to 1.0 × 10 −1 ) molL −1 , with a detection limit of (9.1 ± 0.8) × 10 −10 molL −1 and a Nernstian response of (29.8 ± 0.4) mV decade −1 . This ISE can be used in the 0-6 pH interval, exhibiting a high selectivity toward the mercury ions even in the presence of interferents, and be used as an indicating electrode during potentiometric mercury titration with EDTA, because it is comparable with the commercial electrodes, within its same class. The main advantage of the ISE reported here is its nM LOD and that it does not require an internal reference.

No abstract