Stealth and Biocompatible Gold Nanoparticles through Surface Coating with a Zwitterionic Derivative of Glutathione

Gold nanoparticles (AuNPs) hold promise in biomedicine, but challenges like aggregation, protein corona formation, and insufficient biocompatibility must be thoroughly addressed before advancing their clinical applications. Designing AuNPs with specific protein corona compositions is challenging, and strategies for corona elimination, such as coating with polyethylene glycol (PEG), have limitations. In this study, we introduce a commercially available zwitterionic derivative of glutathione, glutathione monoethyl ester (GSHzwt), for the surface coating of colloidal AuNPs. Particles coated with GSHzwt were investigated alongside four other AuNPs coated with various ligands, including citrate ions, tiopronin, glutathione, cysteine, and PEG. We then undertook a head-to-head comparison of these AuNPs to assess their behavior in biological fluid. GSHzwt-coated AuNPs exhibited exceptional resistance to aggregation and protein adsorption. The particles could also be readily functionalized with biotin and interact with streptavidin receptors in human plasma. Additionally, they exhibited significant blood compatibility and noncytotoxicity. In conclusion, GSHzwt provides a practical and easy method for the surface passivation of AuNPs, creating "stealth" particles for potential clinical applications.

PCR inhibitors and facilitators - Their role in forensic DNA analysis

Since its inception, DNA typing technology has been practiced as a robust tool in criminal investigations. Experts usually utilize STR profiles to identify and individualize the suspect. However, mtDNA and Y STR analyses are also considered in some sample-limiting conditions. Based on DNA profiles thus generated, forensic scientists often opine the results as Inclusion, exclusion, and inconclusive. Inclusion and exclusion were defined as concordant results; the inconclusive opinions create problems in conferring justice in a trial- since nothing concrete can be interpreted from the profile generated. The presence of inhibitor molecules in the sample is the primary factor behind these indefinite results. Recently, researchers have been emphasizing studying the sources of PCR inhibitors and their mechanism of inhibition. Furthermore, several mitigation strategies- to facilitate the DNA amplification reaction -have now found their place in the routine DNA typing assays with compromised biological samples. The present review paper attempts to provide a comprehensive review of PCR inhibitors, their source, mechanism of inhibition, and ways to mitigate their effect using PCR facilitators.

Enhancement of Salmonella Enteritidis Detection Using Nanoparticle-Assisted Real-Time Polymerase Chain Reaction

Improved; fast; and specific detection of pathogens has always been of great importance; more so with the increase of human population and human interaction. In this work we investigate the application of metal oxide nanoparticles (ZnO; Fe2O3; and TiO2) in the detection of the pathogen Salmonella enteritidis using real-time quantitative PCR (qPCR). The nanoparticles were synthesized and characterized; and then they were added at different concentrations to qPCR for Salmonella enteritidis detection. qPCR provides numerical data such as threshold cycle (Ct); efficiency; and DNA yield which make comparing the different tested conditions easier and more accurate. It has been observed that adding all three types of NPs at an optimum concentration 4×10−11 M for ZnO NPs, and 4×10−9 for Fe2O3 and TiO2 nanoparticles has led to increasing the efficiency of the reaction to 100% and to lowering the threshold cycle value by up to 6.6 for ZnO nanoparticles; hence increasing the DNA yield of the reaction; and lowering the detection time of the pathogen by up to 50%.

Capping Gold Nanoparticles to Achieve a Protein-like Surface for Loop-Mediated Isothermal Amplification Acceleration and Ultrasensitive DNA Detection

Loop-mediated isothermal amplification (LAMP) is a popular DNA amplification method. Gold nanoparticles (AuNPs) were reported to enhance the efficiency of LAMP, although the underlying mechanism remained elusive. Since AuNPs strongly adsorb a range of ligands, preadsorbed ligands cannot be easily displaced. In this work, we systematically investigated the effect of surface-modified AuNPs on LAMP by varying the order of mixing of AuNPs with each reagent in the LAMP system (Mg²⁺, template DNA, dNTPs, primers, and polymerase). Mixing the AuNPs with the primers delayed the LAMP based on SYBR green I fluorescence. While other orders of mixing had little effect, all accelerated the reaction. We then tested other common ligands including polymers (polyethylene glycol and polyvinylpyrrolidone), inorganic ions (Br^-), proteins, glutathione (GSH), and DNA (A₁₅) on AuNP-LAMP. The boosted AuNP performance on LAMP was most obvious when the AuNPs formed a protein-like surface. Finally, using GSH-capped AuNPs, a detection limit of around 100 copies/μL^-1 of target DNA was achieved. This work has identified a ligand-capped AuNP strategy to boost LAMP and yielded a higher sensitivity in DNA sensing, which also deepens our understanding of AuNP-assisted LAMP.

The Integration of Gold Nanoparticles with Polymerase Chain Reaction for Constructing Colorimetric Sensing Platforms for Detection of Health-Related DNA and Proteins

Polymerase chain reaction (PCR) is the standard tool in genetic information analysis, and the desirable detection merits of PCR have been extended to disease-related protein analysis. Recently, the combination of PCR and gold nanoparticles (AuNPs) to construct colorimetric sensing platforms has received considerable attention due to its high sensitivity, visual detection, capability for on-site detection, and low cost. However, it lacks a related review to summarize and discuss the advances in this area. This perspective gives an overview of established methods based on the combination of PCR and AuNPs for the visual detection of health-related DNA and proteins. Moreover, this work also addresses the future trends and perspectives for PCR-AuNP hybrid biosensors.

Size and macromolecule stabilizer-dependent performance of gold colloids in immuno-PCR

Gold nanoparticles (GNPs) are well-documented for their size and surface chemistry-dependent electronic and optical properties that are extensively utilized to develop highly sensitive immunoassays. GNP-based immuno-polymerase chain reaction (immuno-PCR) is especially interesting due to the facile loading of biomolecules on the surface of GNP probes and has been utilized to develop analyte-specific assays. In this study, the role of size and surface chemistry of GNPs is explored in detail to develop a highly sensitive and reproducible immuno-PCR assay for specific detection of biotinylated analytes. Our results indicate that smaller-sized gold nanoparticles outperform the larger ones in terms of their sensitivity in immuno-PCR assay and show superior loading of proteins and oligonucleotides on the surface of nanoparticles. Furthermore, the role of different macromolecular stabilizers (such as polyethylene glycol (PEG), bovine serum albumin (BSA), and PEGylated BSA) was compared to optimize the loading of biomolecules and to improve the signal-to-noise ratio of GNP probes. mPEG-BSA-functionalized GNP probes of 15 nm were found to be highly sensitive at low concentrations of analytes and significantly (~ 30 fold) improve the limit of detection of analytes in comparison with ELISA assay.

Lethal effects and ultrastructure of cellular uptake of ingested gold nanoparticles in the freshwater rotifer Brachionus calyciflorus (Monogononta: Brachionidae)

Much of the recent literature concerning the threat posed by anthropogenic microscopic pollution has focussed on marine organisms although freshwater environments face the same degree of pollution and therefore risk. Although several studies have documented the ingestion of nanoparticles (NPs) in species of the pelagic freshwater rotifer genus Brachionus, unambiguous evidence for its cellular uptake in this group remains lacking. We therefore used transmission electron microscopy (TEM) of ultrathin sections through the digestive tract of individuals of Brachionus calyciflorus exposed in vitro to citrate stabilized gold nanoparticles (AuCit NPs) in their culture medium to provide the first concrete evidence for the cellular uptake of NPs in rotifers, a group of organisms that comprise an important part of the zooplankton community. Using this method, AuCit NPs with average diameters of 8.5 ± 1.4 nm and 12.5 ± 1.5 nm could be localized clearly within large vacuoles within the stomach cells. Moreover, the occasional presence of pits containing AuCit NPs in the outer membranes of these cells hints that the particles are taken up by some form of endocytosis. In all cases, the ingestion of AuCit NPs showed lethal effects after only one day with virtually no individuals surviving more than two days of exposure. Combined with the TEM evidence above, we hypothesize that death might derive from some form of lysosomal overload. In total, our results document the potential threat that microscopic pollution also poses for freshwater organisms. Through this, we hope that additional emphasis in this context will be directed toward freshwater environments and the potential for such pollution both to enter as well as to move up the food chain via trophic transfer events.

Nanotechnology-based Colorimetric Approaches for Pathogenic Virus Sensing: A review

Fast and inexpensive virus identification protocols are paramount to hinder the further extent of pandemic diseases, minimize economic and social damages, and expedite proper clinical rehabilitation. Until now, various biosensors have been fabricated for the identification of pathogenic particles. But, they offer many difficulties. Nanotechnology resolves these difficulties and offers direct identification of pathogenic species in real-time. Among them, nanomaterial based-colorimetric sensing approach of pathogenic viruses by the naked eye has attracted much awareness because of their simplicity, speed, and low cost. In this review, the latest tendencies and advancements are overviewed in detecting pathogenic viruses using colorimetric concepts. We focus on and reconsider the use of distinctive nanomaterials such as metal nanoparticles, carbon nanotubes, graphene oxide, and conducting polymer to form colorimetric pathogenic virus sensors.

Quantifying and Adjusting Plasmon-Driven Nano-Localized Temperature Field around Gold Nanorods for Nucleic Acids Amplification

Fast nucleic acid (NA) amplification has found widespread biomedical applications, where high thermocycling rate is the key. The plasmon-driven nano-localized thermocycling around the gold nanorods (AuNRs) is a promising alternative, as the significantly reduced reaction volume enables a rapid temperature response. However, quantifying and adjusting the nano-localized temperature field remains challenging for now. Herein, a simple method is developed to quantify and adjust the nano-localized temperature field around AuNRs by combining experimental measurement and numerical simulation. An indirect method to measure the surface temperature of AuNRs is first developed by utilizing the temperature-dependent stability of Authiol bond. Meanwhile, the relationship of AuNRs' surface temperature with the AuNRs concentration and laser intensity, is also studied. In combination with thermal diffusion simulation, the nano-localized temperature field under the laser irradiation is obtained. The results show that the restricted reaction volume (≈aL level) enables ultrafast thermocycling rate (>10⁴  °C s^-1 ). At last, a duplex-specific nuclease (DSN)-mediated isothermal amplification is successfully demonstrated within the nano-localized temperature field. It is envisioned that the developed method for quantifying and adjusting the nano-localized temperature field around AuNRs is adaptive for various noble metal nanostructures and will facilitate the development of the biochemical reaction in the nano-localized environment.

Machine-Free Polymerase Chain Reaction with Triangular Gold and Silver Nanoparticles

Photothermal effects of metal nanoparticles (NPs) are used for various biotechnological applications. Although NPs have been used in a polymerase chain reaction (PCR), the effects of shape on the photothermal properties and its efficiency on PCR are less explored. The present study reports the synthesis of triangular gold and silver NPs, which can attain temperatures up to ∼90 °C upon irradiation with 808 nm laser. This photothermal property of synthesized nanoparticles was evaluated using various concentrations, irradiation time, and power to create a temperature profile required for variable-temperature PCR. This study reports a cost-effective, machine-free PCR using both gold and silver triangular NPs, with efficiency similar to that of a commercial PCR machine. Interestingly, addition of triangular NPs increases PCR efficiency in commercial PCR reactions. The higher PCR efficiencies are due to the direct binding and unfolding of double-stranded DNA as suggested by circular dichroism and UV spectroscopy. These findings suggest that triangular NPs can be used to develop cost-effective, robust machine-free PCR modules and can be used in various other photothermal applications.

Fast detection of SARS-CoV-2 RNA via the integration of plasmonic thermocycling and fluorescence detection in a portable device

The diagnosis of severe acute respiratory syndrome 2 (SARS-CoV-2) infection by quantitative PCR with reverse transcription (RT-qPCR) typically involves bulky instrumentation in centralized laboratories and an assay time of 1-2 h. Here, we show that SARS-CoV-2 RNA can be detected in 17 min via a portable device integrating reverse transcription, fast thermocycling (via plasmonic heating through magneto-plasmonic nanoparticles) and in situ fluorescence detection following magnetic clearance of the nanoparticles. The device correctly classified all nasopharyngeal, oropharyngeal and sputum samples from 75 patients with COVID-19 and 75 healthy controls, with good concordance in fluorescence intensity with standard RT-qPCR (Pearson coefficients > 0.7 for the N1, N2 and RPP30 genes). Fast, portable and automated nucleic acid detection should facilitate testing at the point of care.

Applications of gold nanoparticles in ELISA, PCR, and immuno-PCR assays: A review

Development of state-of-the-art assays for sensitive and specific detection of disease biomarkers has received significant interest for early detection and prevention of various diseases. Enzyme Linked Immunosorbent assays (ELISA) and Polymerase Chain Reaction (PCR) are two examples of proteins and nucleic acid detection assays respectively, which have been widely used for the sensitive detection of target analytes in biological fluids. Recently, immuno-PCR has emerged as a sensitive detection method, where high specificity of sandwich ELISA assays is combined with high sensitivity of PCR for trace detection of biomarkers. However, inherent disadvantages of immuno-PCR assays limit their application as rapid and sensitive detection method in clinical settings. With advances in nanomaterials, nanoparticles-based immunoassays have been widely used to improve the sensitivity and simplicity of traditional immunoassays. Owing to facile synthesis, surface functionalization, and superior optical and electronic properties, gold nanoparticles have been at the forefront of sensing and detection technologies and have been extensively studied to improve the efficacies of immunoassays. This review provides a brief history of immuno-PCR assays and specifically focuses on the role of gold nanoparticles to improve the sensitivity and specificity of ELISA, PCR and immuno-PCR assays.

An LED-Driven AuNPs-PDMS Microfluidic Chip and Integrated Device for the Detection of Digital Loop-Mediated Isothermal DNA Amplification

The sensitive quantification of low-abundance nucleic acids holds importance for a range of clinical applications and biological studies. In this study, we describe a facile microfluidic chip for absolute DNA quantifications based on the digital loop-mediated isothermal amplification (digital LAMP) method. This microfluidic chip integrates a cross-flow channel for droplet generation with a micro-cavity for droplet tiling. DNA templates in the LAMP reagent were divided into ~20,000 water-in-oil droplets at the cross-flow channel. The droplets were then tiled in the micro-cavity for isothermal amplification and fluorescent detection. Different from the existing polydimethylsiloxane (PDMS) microfluidic chips, this study incorporates gold nanoparticles (AuNPs) into PDMS substrate through silica coating and dodecanol modification. The digital LAMP chip prepared by AuNPs-PDMS combines the benefits of the microstructure manufacturing performance of PDMS with the light-to-heat conversion advantages of AuNPs. Upon illumination with a near infrared (NIR) LED, the droplets were stably and efficiently heated by the AuNPs in PDMS. We further introduce an integrated device with a NIR heating unit and a fluorescent detection unit. The system could detect HBV (hepatitis B virus)-DNA at a concentration of 1 × 10¹ to 1 × 10⁴ copies/μL. The LED-driven digital LAMP chip and the integrated device; therefore, demonstrate high accuracy and excellent performance for the absolute quantification of low-abundance nucleic acids, showing the advantages of integration, miniaturization, cost, and power consumption.

Gold@Silica Nanoparticles Functionalized with Oligonucleotides: A Prominent Tool for the Detection of the Methylated Reprimo Gene in Gastric Cancer by Dynamic Light Scattering

Reprimo (RPRM) is a tumor suppressor gene involved in the development of gastric cancer. Hypermethylation of the RPRM promoter region has been found in tumor tissue and plasma samples from patients with gastric cancer. These findings suggest that circulating methylated DNA of RPRM could be a candidate for a noninvasive detection of gastric cancer. We designed a nanosystem based on the functionalization of silica coated gold nanoparticles with oligonucleotides that recognize a specific DNA fragment of the RPRM promoter region. The functionality of the oligonucleotide on the surface of the nanoparticle was confirmed by polymerase chain reaction (PCR). The nanoparticles were incubated with a synthetic DNA fragment of methylated DNA of RPRM and changes in the size distribution after hybridization were evaluated by dynamic light scattering (DLS). A difference in the size distribution of nanoparticles hybridized with genomic DNA from the KATO III gastric cancer cell line was observed when was compared with DNA from the GES-1 normal cell line. These results showed that this nanosystem may be a useful tool for the specific and sensitive detection of methylated DNA of RPRM in patients at risk of developing gastric cancer.

Enhancement of the polymerase chain reaction by tungsten disulfide

In this paper, we demonstrated that the polymerase chain reaction (PCR) could be dramatically enhanced by tungsten disulfide (WS₂). The results showed that the PCR efficiency could be increased with the addition of WS₂ and at a lower annealing temperature, which simplified the design and operation of PCR. Moreover, PCR with WS₂ showed better specificity and efficiency as compared with graphene oxide (GO) for a human genome DNA sample. The mechanism of enhancement of PCR by WS₂ was discussed according to the typical structure and the characteristics of selective adsorption of single-stranded DNA by WS₂. The results suggested that WS₂ as a PCR enhancer can promote the PCR performance and extend the PCR application in biomedical research, clinical diagnostic, and bioanalysis.

WS₂ as a PCR enhancer can promote the PCR performance and extend PCR bioapplication.

Colorimetric detection of heparin with high sensitivity based on the aggregation of gold nanoparticles induced by polymer nanoparticles

The negatively charged heparin hinders the aggregation of Au nanoparticles induced by the cationic polymer nanodots.