The development of improved methods for the synthesis of monodisperse gold nanoparticles (Au NPs) is of high priority because they can be used as substrates for surface-enhanced Raman scattering (SERS) applications relating to biological lipids. Herein, Au NPs have been successfully synthesized via a seed-mediated growth method. The LSPR peak is controlled via adjusting the gold nanoseed component, and different fabrication methods were studied to establish the effect of sonication time on NP size. The simple, facile, and room-temperature method is based on a conventional ultrasonic bath, which leads to ultrasonic energy effects on the size and morphology of the Au NPs. This research offers new opportunities for the production of highly monodispersed spherical Au NPs without the use of a magnetic stirrer method, as evidenced by ultraviolet-visible reflectance spectra and scanning electron microscopy (SEM) analysis. SEM images indicate that the spherical Au NP colloidal particles are stable and reliable, which paves the way for their use as a nanostructured biosensor platform that can be exploited for multiple applications, for example, in materials science, sensing, catalysis, medicine, food safety, biomedicine, etc. The highest enhancement factor that could be achieved in terms of the SERS enhancement activity of these Au NP arrays was determined using 10⁻⁹ M serotonin (5-hydroxytryptamine, 5-HT) as the Raman probe molecules.

Accurate and rapid blood-based detection of dopamine levels can aid in the diagnosis and monitoring of diseases related to dopaminergic dysfunction. For the sensitive detection of dopamine levels in human blood plasma (i.e., plasma dopamine levels), a silver-plated Au bimetallic nanocluster (so called plasmonic Au/Ag nanocluster) was prepared as a surface-enhanced Raman scattering (SERS) substrate by the combination of electrodeposition and electroless plating methods. The plasmonic effect of the Au/Ag nanocluster substrate was optimized by controlling the particle morphology, packing density, and interparticle distance, showing the best performance in its SERS activity. The lowest detection limit of dopamine was ∼10⁻¹¹ M. A linear standard curve was obtained by plotting the log-scale of dopamine concentration (log C) versus Raman intensity at 1152 cm⁻¹. The optimized SERS substrate quantified the plasma dopamine levels of patients with antipsychotic drug-induced Parkinsonism (n = 15) as 3.24 × 10⁻⁹ M and healthy control subjects (n = 15) as 2.31 × 10⁻⁸ M. Patients with drug-induced Parkinsonism had ∼86% lower plasma dopamine concentration than healthy subjects (two-tailed p-value = 0.000002), indicating a clear separation between the groups. Our study provides the first report on the quantitative SERS detection of dopamine levels in human blood plasma with Parkinsonism. The results highlight the potential clinical utility of the optimized SERS technique in screening clinical populations with dopaminergic dysfunction, i.e., differentiating between healthy subjects and patients with Parkinsonism.

Lemongrass essential oil has many compounds appropriate for application in foods, cosmetics, and pharmaceutical products. Of these, citral is a high-value compound of interest to industry. This work aims to evaluate the use of vacuum fractional distillation to separate lemongrass essential oil compounds, producing essential oil fractions containing high citral content. The effect of process parameters, namely vacuum pressure, type column, and energy input, on the fractionation time, content, and recovery of citral in the fractions, was investigated. The fractionation of lemongrass oils successfully provided five fractions, i.e., fraction 1 (F1), fraction 2 (F2), fraction 3 (F3), fraction 4 (F4), and fraction 5 (F5). GC-MS (Gas Chromatography-Mass Spectrometry) spectra showed that the main compound contained in F1 and F2 fractions was β-myrcene (>70%). Meanwhile, F4 and F5 were the two main fractions for citral recovery. The optimal conditions of the fractional distillation system included a column height of 400 mm, power input of 165 W, and pressure of 15 mmHg. These conditions correspond to the highest total citral content of 95%, with a recovery of 80% at the F4 and F5 fractions. Therefore, fractional vacuum distillation may be an effective method to upgrade lemongrass essential oil.

Nowadays, virus pandemics have become a major burden seriously affecting human health and social and economic development. Thus, the design and fabrication of effective and low-cost techniques for early and accurate virus detection have been given priority for prevention and control of such pandemics. Biosensors and bioelectronic devices have been demonstrated as promising technology to resolve the major drawbacks and problems of the current detection methods. Discovering and applying advanced materials have offered opportunities to develop and commercialize biosensor devices for effectively controlling pandemics. Along with various well-known materials such as gold and silver nanoparticles, carbon-based materials, metal oxide-based materials, and graphene, conjugated polymer (CPs) have become one of the most promising candidates for preparation and construction of excellent biosensors with high sensitivity and specificity to different virus analytes owing to their unique π orbital structure and chain conformation alterations, solution processability, and flexibility. Therefore, CP-based biosensors have been regarded as innovative technologies attracting great interest from the community for early diagnosis of COVID-19 as well as other virus pandemics. For providing precious scientific evidence of CP-based biosensor technologies in virus detection, this review aims to give a critical overview of the recent research related to use of CPs in fabrication of virus biosensors. We emphasize structures and interesting characteristics of different CPs and discuss the state-of-the-art applications of CP-based biosensors as well. In addition, different types of biosensors such as optical biosensors, organic thin film transistors (OTFT), and conjugated polymer hydrogels (CPHs) based on CPs are also summarized and presented.

Because dopamine (DA) is one of the most critical neurotransmitters that influence a wide variety of motivated human behaviors, it is necessary to develop a facile diagnostic tool that can quantify the physiological level. In this study, core–shell magnetic silica nanoparticles (Fe3O4@SiO2) were prepared using a modified sol–gel reaction. The Fe3O4@SiO2 were functionalized using 3-aminophenylboronic acid (APBA) via a facile and rapid synthetic route, hereafter referred to as Fe3O4@SiO2@APBA The resultant Fe3O4@SiO2@APBA not only adsorbed DA molecules, but also were easily separated from solution using a simple magnetic manipulation. The adsorbed amounts of DA by the Fe3O4@SiO2@APBA were quantified by measuring the changes in fluorescence intensity of polydopamine (at 463 nm) originated from the self-polymerized DA remained in the supernatant before and after the adsorption process. The Fe3O4@SiO2@APBA exhibited two-stage adsorption behavior for DA, and the maximal adsorption capacity was 108.46 μg/g at pH 8.5. Our particle system demonstrated the potential application for extracting compounds with cis-diols (including catechol amines) from the biological fluid.