Tris stabilized AuNPs based lateral flow immunochromatography for the simultaneous detection of porcine epidemic diarrhea virus and rotavirus on-site

Porcine epidemic diarrhea virus (PEDV) and rotavirus has posed a significant threat to the pig industry annually across different nations, resulting in huge economic losses. The frequent co-infection of these two viruses in clinical settings complicates the process of differential diagnoses. Rapid and accurate detection of PEDV and rotavirus is in great demand for timely diarrhea disease prevention and control. In this study, tris stabilized AuNPs were prepared and a sensitive lateral flow immunoassay (LFIA) sensor was developed for the simultaneous and rapid detection of PEDV and rotavirus on site. After the system optimization, the established LFIA can simultaneously identify PEDV and rotavirus with limits of detection (LOD) of 1.25 × 103 TCID50 mL-1 and 3.13 × 102 pg mL-1, respectively. When applying for clinical samples, the LFIA show a concordance of 95 % and 100 % to reverse transcript polymerase chain reaction (RT-PCR) for PEDV and rotavirus respectively. Therefore, this LFIA can qualitatively detect PEDV and rotavirus in 18 min with high sensitivity and accuracy without any sophisticated equipment and operation, making it a promising candidate for the early diagnosis of PEDV or/and rotavirus diarrhea on site.

SERS-Temperature Dual-Mode T-type Lateral Flow Strip for Accurate Detection of Free and Total Prostate-Specific Antigens in Blood

Accurate point-of-care (POC) analysis of cancer markers is the essence in the comprehensive early screening and treatment of cancer. Dual-mode synchronous detection is one of the effective approaches to reduce the probability of false negatives or false positives. As a result, this can greatly improve the accuracy of diagnosis. In this work, a surface-enhanced Raman scattering (SERS)-temperature dual-mode T-type lateral flow strip was fabricated to direct and simultaneous POC detection of total and free prostate-specific antigens (t-PSA and f-PSA) in blood. With the advantage of high stability of T-type lateral flow strip and simultaneous acquirement of assay results for t-PSA and f:t PSA ratio, the proposed method has high accuracy in the diagnosis of prostate cancer, especially in the diagnostic gray zone between 4.0 and 10.0 ng/mL. The SERS-temperature dual-signal has a good linear correlation with either f-PSA or t-PSA. To evaluate the clinical diagnostic performance of the proposed method, spiked human serum samples and the whole blood sample were analyzed. The assay results showed good recovery, and compared with traditional electrochemiluminescence immunoassay (ECLIA) method (t-PSA: 43.151; f/t ratio: 0.08), the results obtained by the proposed method were similar (t-PSA: 40.15 (SERS), 36.21 (temperature); f/t ratio: 0.08 (SERS), 0.08 (temperature), but the detection time (15 min) and cost ($0.05) had been greatly reduced. Therefore, the proposed SERS-temperature synchronous dual-mode T-type lateral flow strip has a strong application potential in the field of accurate large-scale diagnostics of prostate cancer on-site by simultaneous POC detection of t-PSA and f-PSA in blood.

A detection method for Prorocentrum minimum by an aptamer-gold nanoparticles based colorimetric assay

Here, to give early waring for harmful algal blooms caused by Prorocentrum minimum, we reported a simple and rapid colorimetric assay that is named aptamer-gold nanoparticles (GNPs) based colorimetric assay (AGBCA). The GNPs maintain a dispersed state and have a strong characteristic absorption peak at 520 nm. With the addition of NaCl, the stability of the solution will be destroyed and the dispersed GNPs will aggregate. Therefore, the characteristic absorption peak of the GNPs solution will change from 520 nm to 670 nm. Aptamers can be adsorbed on the surface of GNPs, effectively preventing the aggregation of GNPs. In the presence of P. minimum, aptamers will specifically bind to P. minimum, causing the dissociation of the aptamers from GNPs. Consequently, the GNPs will aggregate in the NaCl solution, corresponding to a new absorption peak at 670 nm. A linear relationship between the absorbance ratio variation (ΔA₆₇₀/A₅₂₀) and the P. minimum concentration was observed in the concentration range of 1 × 10² - 1 × 10⁷ cells mL^-1, with a low detection limit of 8 cells mL^-1. The developed AGBCA is characterized by simplicity, strong specificity, and high sensitivity and is thus promising for the quantitative detection of P. minimum in natural samples.

Water-Soluble Photoluminescent Adenosine-Functionalized Gold Nanoclusters as Highly Sensitive and Selective Receptors for Riboflavin Detection in Rat Brain

Simple, selective, and sensitive detection of cerebral riboflavin is of great significance due to the vital roles of riboflavin in physiological and pathological processes. In the work, water-soluble photoluminescent adenosine-functionalized gold nanoclusters (Ade-AuNCs) are exploited as highly sensitive and selective receptors for cerebral riboflavin detection. The Ade-AuNCs are prepared under aqueous conditions by the one-step "synthesis-functionalization integration" strategy, using chloroauric acid as gold precursors and adenosine as outer-shell ligands. During the Ade-AuNCs synthesis process, adenosine and ascorbic acid are demonstrated to respectively serve as a stabilizer and a reductant, and citrate buffer plays multiple roles including a pH regulator, reductant, and complexing agent. The added riboflavin causes photoluminescence quenching of Ade-AuNCs, and the quenching photoluminescence is applied for well quantifying riboflavin in the range of 0.005-0.1 nM with a detection limit of 0.002 nM. The detailed analytical characterizations reveal that the photoluminescence quenching results from the static photoinduced electron transfer process from the surface functional Ade-AuNCs to riboflavin and the strong affinity between Ade-AuNCs and riboflavin. Moreover, the Ade-AuNC-based sensor exhibits a high selectivity for riboflavin over metal ions, anions, amino acids, and biological substances that possibly exist in the rat brain. Finally, by coupling the microdialysis technique, the proposed sensor is successfully applied to detect riboflavin in living rat brain microdialysates with a basal value of 13.1 ± 2.5 nM (n = 3), and the results are comparable well with those from a reference high-performance liquid chromatography method.

Role of Solvent in Electron-Phonon Relaxation Dynamics in Core-Shell Au-SiO2 Nanoparticles

Relaxation dynamics of plasmons in Au-SiO₂ core-shell nanoparticles have been followed by femtosecond pump-probe technique. The effect of excitation pump energy and surrounding medium on the time constants associated with the hot electron relaxation has been elucidated. A gradual increase in the electron-phonon relaxation time with pump energy is observed and can be attributed to the higher perturbation of the electron distribution in AuNPs at higher pump energy. Variation in time constants for the electron-phonon relaxation in different solvents is rationalized on the basis of their thermal conductivities, which govern the rate of dissipation of heat of photoexcited electrons in the nanoparticles. On the other hand, phonon-phonon relaxation is found to be much less effective than electron-phonon relaxation for the dissipation of energy of the excited electron and the time constants associated with it remain unaffected by thermal conductivity of the solvent.

Macroscopic Au@PANI Core/Shell Nanoparticle Superlattice Monolayer Film with Dual-Responsive Plasmonic Switches

The self-assembled gold nanoparticle (NP) superlattice displays unusual but distinctive features such as high mechanical and free-standing performance, electrical conductivity, and plasmonic properties, which are widely employed in various applications especially in biological diagnostics and optoelectronic devices. For a two-dimensional (2D) superlattice monolayer film composed of a given metal nanostructure, it is rather challenging to tune either its plasmonic properties or its optical properties in a reversible way, and it has not been reported. It is therefore of significant value to construct a free-standing 2D superlattice monolayer film of gold nanoparticles with an intelligent response and desired functions. Herein, we developed an easy and efficient approach to construct a gold nanoparticle superlattice film with a dual-responsive plasmonic switch. In this system, gold nanoparticles were coated by polyaniline (PANI) and then interracially self-assembled into a monolayer film at the air-liquid interface. The PANI shell plays two important roles in the superlattice monolayer film. First, the PANI shell acts as a physical spacer to provide a steric hindrance to counteract the van der Waals (vdW) attraction between densely packed nanoparticles (NPs), resulting in the formation of a superlattice by adjusting the thickness of the PANI shell. Second, the PANI shells provide the superlattice film with multiple stimuli such as electrical potential and pH change, leading to reversible optical and plasmonic responsiveness. The superlattice monolayer film can show a vivid color change from olive green to pink, or from olive green to violet by the change of the corresponding stimuli. Also, the localized surface plasmonic resonance (LSPR) of the superlattice monolayer film can be reversibly modulated by both by changing the local pH and applying an electric potential. Notably, a significant plasmonic shift of 157 nm can be achieved in the superlattice monolayer film when the PANI shell with a thickness of 35 nm and gold nanorods as a core were used. The superlattice monolayer film with dual-responsive plasmonic switches is promising for a range of potential applications in optoelectronic devices, plasmonic and colorimetric sensors, and surface-enhanced Raman scattering (SERS).

Free-Standing 2D Janus Gold Nanoparticles Monolayer Film with Tunable Bifacial Morphologies via the Asymmetric Growth at Air-Liquid Interface

Large scaled two-dimensional free-standing monolayer films of gold nanoparticles show distinctive optical, electrical, and chem-physical propertie making them a new class of advanced plasmonic materials differing from bulk materials and individual nanoparticles in solution. The conventional 2D gold nanoparticle films usually possess symmetric structures and identical properties of gold nanoparticles on both sides. Herein, we developed an easy and efficient approach to construct a new type of free-standing 2D gold nanoparticle monolayer film with asymmetric gold nanoparticle structures and functions, called a 2D Janus gold nanoparticle film. The remarkable feature of our method is the subsequent asymmetric growth on one side of the interfacial self-assembled gold nanoparticle monolayer film at the air-liquid interface. It is very easy to control the morphology of the Janus film by simply and precisely adjusting the size and shape of the gold nanoparticles on the top side, and selectively tuning the structure and composition on the bottom side of the film by growing gold nanoparticles or other noble metals such as Ag, Pt, and Pd. Unlike the conventionally prepared Janus films at solid substrate that require long-time etching and transfer procedures, other features of our method include the short time in which the interfacial self-assembly and the subsequent asymmetric growth are completed as well as the easily transferable property of the Janus film onto different substrates, such as quartz glass sheets, silicon wafers, and PDMS. The obtained Janus gold nanoparticle film shows asymmetric wettabilities, optical properties, and surface-enhanced Raman scattering (SERS) effects, which is promising for a range of potential applications in optical devices, sensors, and asymmetric catalysis.

Comparative study of antidiabetic, bactericidal, and antitumor activities of MEL@AgNPs, MEL@ZnONPs, and Ag-ZnO/MEL/GA nanocomposites prepared by using MEL and gum arabic

In this study, a variety of nanocomposites, namely, MEL@AgNPs, MEL@ZnONPs, and Ag-ZnO/MEL/GA were biosynthesized using MEL and gum arabic to serve in biomedical applications. The synthesized nanocomposites were examined using X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and FTIR spectroscopy. The physicochemical properties and biomedical activities of the synthesized nanocomposites were investigated. The Ag-ZnO/MEL/GA nanocomposites showed greater antidiabetic activity against α-amylase and α-glucosidase, and higher antibacterial activity compared to MEL@AgNPs and MEL@ZnONPs. Furthermore, HepG2 cells were exposed to MEL@AgNPs, MEL@ZnONPs, and Ag-ZnO/MEL/GA nanocomposites for 24 h and their IC50 values were 63.25, 26.91 and 28.97 μg mL-1 (P < 0.05), respectively. According to this comparative study, it is apparent that the Ag-ZnO/MEL/GA nanocomposites have a great potential to serve as antitumor agents against HepG2, and antidiabetic and antibacterial agents.

pH and Temperature Dual-Responsive Plasmonic Switches of Gold Nanoparticle Monolayer Film for Multiple Anticounterfeiting

Two-dimensional (2D) gold nanoparticle (Au NP) monolayer film possesses a lot of fascinating peculiarities, and has shown promising applications in photoelectrical devices, catalysis, spectroscopy, sensors, and anticounterfeiting. Because of the localized surface plasmon resonance (LSPR) property predetermined by the natural structure of metal nanoparticles, it is usually difficult to realize the reversible LSPR transition of 2D film. In this work, we report on the fabrication of a large-area free-standing Au NP monolayer film with dual-responsive switchable plasmonic property using a pH- or thermal-responsive dendronized copolymer as a stimuli-sensitive linker. In this system, an oligoethylene-glycol-based (OEG-based) dendronized copolymer (named PG1A) with pH or temperature sensitivity was first modified onto the surface of a Au NP. Then, polyethylene glycol dibenzyl aldehyde (PEG-DA) was introduced to interact with the amino moieties from PG1A before the process of oil-water interfacial self-assembly of NPs, resulting in an elastic, robust, pH- or temperature-sensitive interpenetrating network among Au NPs in monolayer films. In addition, the film could exhibit reversibly plasmonic shifts of about 77 nm and inherent color changes through varying temperature or pH. The obtained free-standing monolayer film also shows an excellent transferable property, which can be easily transferred onto substrates such as plastic molds, PDMS, copper grids, and silicon wafers. In virtue of these peculiarities of the free-standing property, special plasmonic signal, and homologous macroscopic color, the transferred film was primely applied to an anticounterfeiting security label with clear color change at the designed spots, providing a new avenue to plasmonic nanodevices with various applications.