Fast and Facile Etching of Gold Nanorods by N-Halosuccinimides: Toward Multicolorimetric Identification and Quantification of 20 Natural Amino Acids.

Gold nanorods (AuNRs) have recently become fascinating chromophores in the field of colorimetric sensing because of their eye-catching rainbow colors along with the high dimensionality of their optical profile. The etching of AuNRs using an analyte-sensitive oxidizing agent is particularly an attractive tool not only for adjusting their plasmonic behavior through altering their aspect ratio but also for correlating the observed signal with the identity and concentration of the analyte. However, the deployment of this strategy in the field of sensing has been seriously hindered by various factors ranging from slow etching kinetics and the need for nonambient temperatures to low degrees of controllability along with the high toxicity of the etchants. To resolve these challenges, the present study aims to introduce the outstanding potentials of two inexpensive mild oxidants comprising N-bromosuccinimide (NBS) and N-chlorosuccinimide (NCS) in the highly fast and controllable etching of AuNRs at room temperature. By controlling the concentration of the etchant and the pH of the medium, the longitudinal and transversal peaks could be well adjusted with nanometer precision. In an attempt to elucidate the etching mechanism, the effects of various parameters including the etchant concentration and pH, as well as the kinetics of the etching process were thoroughly investigated. After all, the capability of NBS in decarboxylating the amino acids was further exploited in the design of an all-inclusive multicolorimetric sensor array based on the etching of AuNRs for the sensitive quantification and highly accurate discrimination of all 20 amino acids in the micromolar range. To this end, the acquired data set was analyzed by two machine learning techniques including partial least-squares regression (PLSR) and linear discriminant analysis (LDA). The versatility of N-halosuccinimide reactions with various categories of organic compounds underlies ample opportunities for the design of diverse multicolorimetric sensors, further glamorizing the prospect of this approach.

Nanoplasmonic Decoration of Sacrificial Bacteria: Directing Interparticle Coupling Toward Multiplex Analysis of Antiseptic Alcohols.

Engineering interparticle plasmon coupling through controlling the assembly of plasmonic NPs onto the surface of sacrificial substrates is quite promising for establishing inherently absent selectivity or sensitivity toward a particular analyte. Herein, we introduce a robust sensor array strategy based upon the assembly of gold nanoparticles (AuNPs) on the cysteamine-modified surface of two Gram-positive probiotic bacteria, i.e., Lactobacillus reuteri (LBR) and Bifidobacterium lactis (BFL), as potential sacrificial substrates, for discrimination and quantification of antiseptic alcohols (AAs) comprising methanol, ethanol, and isopropanol. In fact, the damage of the bacterial membrane upon exposure to the foregoing alcohols inhibits the assembly of AuNPs, thereby precluding color variations from red to blue. Unequal resistance of the bacterial membranes against damage by the alcohols underlies independent response patterns for each analyte. The supervised classification of visible spectra and RGB data by Linear Discriminant Analysis (LDA) revealed the remarkable potential of the designed sensor array in differentiating single-component and multicomponent samples of AAs. Moreover, the Partial Least Square Regression (PLSR) technique exhibited excellent applicability to multivariate calibration of both spectral and RGB data. The intriguing attributes of the implemented approach not only hold great potential in the authentication and quality assessment of alcohol-based products but open up a new prospect for deployment of sacrificial substrates in the design of interparticle coupling-based sensors.

Self-assembled graphene-based microfibers with eclectic optical properties.

The construction of graphene-based microfibers with reinforced mechanical and electrical properties has been the subject of numerous researches in recent years. However, the fabrication of graphene-based fibers with remarkable optical features still remains a challenge and has not been addressed so far. This paper aims to report a series of flexible self-assembled fibers, synthesized through a few-minute sonication of thermally oxidized graphene oxide nanosheets, so-called Nanoporous Over-Oxidized Graphene (NOG), in an acidic medium. These free-standing glassy fibers were classified into four distinct morphological structures and displayed a collection of intriguing optical properties comprising high transparency, strong birefringence, fixed body colorations (e.g. colorless, blue, green, and red), tunable interference marginal colorations, UV-visible-near IR fluorescence, and upconversion emissions. Moreover, they exhibited high chemical stability in strongly acidic, basic, and oxidizing media. The foregoing notable attributes introduce the NOG fiber as a promising candidate both for the construction of graphene-based photoluminescent textiles and the development of a wide variety of optical applications.

Betulin and its derivatives as novel compounds with different pharmacological effects.

Betulin (B) and Betulinic acid (BA) are natural pentacyclic lupane-structure triterpenoids which possess a wide range of pharmacological activities. Recent evidence indicates that B and BA have several properties useful for the treatment of metabolic disorders, infectious diseases, cardiovascular disorders, and neurological disorders. In the current review, we discuss B and BA structures and derivatives and then comprehensively explain their pharmacological effects in relation to various diseases. We also explain antiviral, antibacterial and anti-cancer effects of B and BA. Finally, we discuss the delivery methods, in which these compounds most effectively target different systems.