Kirigami tripod-based electrode for the development of highly stretchable dengue aptasensor.

Kirigami is one of the interesting paper art forms and the modified sub-class of origami. Kirigami paper art is widely employed in a variety of applications, and it is currently being used in biosensors because of its outstanding advantages. This is the first study on the use of a Kirigami-based aptasensor for DENV (Dengue virus)-antigen detection. In this study, the kirigami approach has been utilized to develop a stretchable, movable, and flexible sensor. The constructed stretchable-kirigami electrode helps in adjusting the connection of electrodes without disturbing the electrochemical cell zone during the experiment. To increase the sensitivity of this biosensor we have synthesized Ag-NPs (Silver nanoparticles) via chemical methods and characterized their results with the help of TEM & UV-Vis Spectroscopy. Different electrochemical approaches were used to validate the sensor response i.e., CV (Cyclic voltammetry) and LSV (Linear sweep voltammetry), which exhibited great detection capability towards dengue virus with the range of 0.1 µg/ml to 1000 µg/ml along with a detection limit of 0.1 µg/ml and showing no reactivity to the chikungunya virus antigen, making it more specific to the DENV antigen. Serum (healthy-human) was also successfully applied to validate the results of the constructed aptasensor. Integration of the Kirigami approach form with the electrochemical aptasensor that utilizes a 3-E setup (three-electrode setup) which is referred to as a tripod and collectively called Kirigami-tripod-based aptasensor. Thus, the developed integrated platform improves the sensors capabilities in terms of cost efficiency, high stretchability, and sensitivity.

Local hyperthermia mediated by gold nanoparticle-integrated silicone-covered stent: feasibility and tissue response in a rat esophageal model.

BACKGROUND: To assess the feasibility and tissue response of using a gold nanoparticle (AuNP)-integrated silicone-covered self-expandable metal stent (SEMS) for local hyperthermia in a rat esophageal model. METHODS: The study involved 42 Sprague-Dawley rats. Initially, 6 animals were subjected to near-infrared (NIR) laser irradiation (power output from 0.2 to 2.4 W) to assess the in vitro heating characteristics of the AuNP-integrated SEMS immediately after its placement. The surface temperature of the stented esophagus was then measured using an infrared thermal camera before euthanizing the animals. Subsequently, the remaining 36 animals were randomly divided into 4 groups of 9 each. Groups A and B received AuNP-integrated SEMS, while groups C and D received conventional SEMS. On day 14, groups A and C underwent NIR laser irradiation at a power output of 1.6 W for 2 min. By days 15 (3 animals per group) or 28 (6 animals per group), all groups were euthanized for gross, histological, and immunohistochemical analysis. RESULTS: Under NIR laser irradiation, the surface temperature of the stented esophagus quickly increased to a steady-state level. The surface temperature of the stented esophagus increased proportionally with power outputs, being 47.3 ± 1.4 °C (mean ± standard deviation) at 1.6 W. Only group A attained full circumferential heating through all layers, from the epithelium to the muscularis propria, demonstrating marked apoptosis in these layers without noticeable necroptosis. CONCLUSIONS: Local hyperthermia using the AuNP-integrated silicone-covered SEMS was feasible and induced cell death through apoptosis in a rat esophageal model. RELEVANCE STATEMENT: A gold nanoparticle-integrated silicone-covered self-expanding metal stent has been developed to mediate local hyperthermia. This approach holds potential for irreversibly damaging cancer cells, improving the sensitivity of cancer cells to therapies, and triggering systemic anticancer immune responses. KEY POINTS: • A gold nanoparticle-integrated silicone-covered self-expanding metal stent was placed in the rat esophagus. • Upon near-infrared laser irradiation, this stent quickly increased the temperature of the stented esophagus. • Local hyperthermia using this stent was feasible and resulted in cell death through apoptosis.

Analysis of Optimal Treatment Starting Time for Photothermal Therapy Through Analysis of Diffusion Behavior of Gold Nanoparticles.

Introduction: Due to its distinct advantage of non-invasive application in treatment, photothermal therapy (PTT) is being studied by many researchers to reduce the need for surgical incisions. It is characterized by the injection of nanoparticles into biological tissue as photothermal agents (PTAs) which diffuse within the tissue. In this study, the diffusion behavior of various doses of gold nanoparticles (AuNPs) injected into tumor tissues is analyzed and the effectiveness of PTT at each elapsed time after injection is confirmed by numerical analysis. Methods: The diffusion behavior of AuNPs within biological tissues is assessed using the convection-diffusion equation, while the temperature distribution is determined using the Pennes bioheat transfer equation. In addition, the effect of the diffusion behavior of AuNPs on the effectiveness of PTT is quantitatively confirmed by analyzing the temperature distribution in the medium through the apoptotic variable. Numerical simulation parameters are selected with doses ranging from 100 to 400 µg/mL, elapsed time after injection from 1 min to 24 h, and laser power ranging from 0 to 1 W. Results: After evaluating PTT's efficacy in every situation, it was discovered that a dosage of 100-300 µg/mL produced the best therapeutic result, with the highest impact occurring 12 hours after injection. In contrast, when the dosage was 400 µg/mL, the highest therapeutic effect was achieved after 18 hours post-injection. Additionally, it was discovered that the ideal laser power at each injection dose was 0.22, 0.14, 0.12, and 0.12 W, respectively. Conclusion: The conditions required to achieve the optimal treatment effect at each dosage, presented here, are expected to accelerate the commercialization of PTT.

Plasmonic Annular Nanotrenches with 1 nm Nanogaps for Detection of SARS-CoV-2 Using SERS-Based Immunoassay.

This study represents the synthesis of a novel class of nanoparticles denoted as annular Au nanotrenches (AANTs). AANTs are engineered to possess embedded, narrow circular nanogaps with dimensions of approximately 1 nm, facilitating near-field focusing for detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) via a surface-enhanced Raman scattering (SERS)-based immunoassay. Notably, AANTs exhibited an exceedingly low limit of detection (LOD) of 1 fg/mL for SARS-CoV-2 spike glycoproteins, surpassing the commercially available enzyme-linked immunosorbent assay (ELISA) by 6 orders of magnitude (1 ng/mL from ELISA). To assess the real-world applicability, a study was conducted on 50 clinical samples using an SERS-based immunoassay with AANTs. The results revealed a sensitivity of 96% and a selectivity of 100%, demonstrating the significantly enhanced sensing capabilities of the proposed approach in comparison to ELISA and commercial lateral flow assay kits.

Gold nanoparticles exhibit anti-osteoarthritic effects via modulating interaction of the "microbiota-gut-joint" axis.

Osteoarthritis (OA) is a common degenerative joint disease that can cause severe pain, motor dysfunction, and even disability. A growing body of research indicates that gut microbiota and their associated metabolites are key players in maintaining bone health and in the progression of OA. Short-chain fatty acids (SCFAs) are a series of active metabolites that widely participate in bone homeostasis. Gold nanoparticles (GNPs) with outstanding anti-bacterial and anti-inflammatory properties, have been demonstrated to ameliorate excessive bone loss during the progression of osteoporosis (OP) and rheumatoid arthritis (RA). However, the protective effects of GNPs on OA progression are not clear. Here, we observed that GNPs significantly alleviated anterior cruciate ligament transection (ACLT)-induced OA in a gut microbiota-dependent manner. 16S rDNA gene sequencing showed that GNPs changed gut microbial diversity and structure, which manifested as an increase in the abundance of Akkermansia and Lactobacillus. Additionally, GNPs increased levels of SCFAs (such as butyric acid), which could have improved bone destruction by reducing the inflammatory response. Notably, GNPs modulated the dynamic balance of M1/M2 macrophages, and increased the serum levels of anti-inflammatory cytokines such as IL-10. To sum up, our study indicated that GNPs exhibited anti-osteoarthritis effects via modulating the interaction of "microbiota-gut-joint" axis, which might provide promising therapeutic strategies for OA.

SILAR Growth of ZnO NSs/CdS QDs on the Optical Fiber-Based Opto-Electrode with Guided In Situ Light and Its Application for the "Signal-On" Detection of Inflammatory Cytokine.

In this study, a novel integrated photoelectrochemical (PEC) sensor platform was proposed, utilizing an optical fiber (OF) as the working electrode for guided in situ light. A CdS quantum dots (QDs)/ZnO nanosheets (NSs) n-n heterojunction was quickly and easily constructed on the OF surface by successive ionic layer adsorption and reaction (SILAR). Au nanoparticles (NPs)@dsDNA as a capturing probe were modified on the CdS QDs/ZnO NSs@OF (CZ@OF). Due to the energy transfer between Au NPs@dsDNA and CdS QDs, the resultant opto-electrode has a lower background near zero, enabling the "signal-on" detection of biomarkers (interleukin-6 (IL-6) as a model). The OF-PEC biosensor demonstrated a wide linear range from 1 to 100 pg mL-1 with a regression coefficient (R2) of 0.9958 and an impressive detection limit (LOD) of 0.19 pg mL-1. More significantly, the proposed OF-PEC can be successfully used for the detection of IL-6 in serum samples from patients with pulmonary arterial hypertension, and it showed consistency and is more sensitive to trace concentrations compared to BD FACSCanto II flow cytometry used at the hospital. This holds significance for an early disease diagnosis. Therefore, the proposed OF-PEC not only achieves integration of the light source and sensing interface but also enables sensitive and accurate "signal-on" detection of IL-6. Furthermore, due to the flexibility and remote detection capabilities of OF, the application of OF-PEC is expected to be expanded more widely. This approach opens up possibilities for advances in PEC sensing.

Self-assembly of a AuNPs/Ti3C2 MXene hydrogel for cascade amplification of microRNA-122 biosensing.

A three-dimensional (3D) self-assembled AuNPs/Ti3C2 MXene hydrogel (AuNPs/Ti3C2 MXH) nanocomposite was prepared for the fabrication of a novel microRNA-122 electrochemical biosensor. The 3D hydrogel structure was gelated from two-dimensional MXene nanosheets with the assistance of graphite oxide and ethylenediamine. MXene hydrogels supported the in situ formation of Au nanoparticles (AuNPs) that predominantly exploring the (111) facet, and these AuNPs are utilized as carriers for hairpin DNA (hpDNA) probes, facilitating DNA hybridization. MXene acted as both a reductant and stabilizer, significantly improving the electrochemical signal. In addition, the conjugation of PAMAM dendrimer-encapsulated AuNPs and H-DNA worked as an ideal bridge to connect targets and efficient electrochemical tags, providing a high amplification efficiency for the sensing of microRNA-122. A linear relationship between the peak currents and the logarithm of the concentrations of microRNA-122 from 1.0 × 10-2 to 1.0 × 102 fM (I = 1.642 + 0.312 lgc, R2 = 0.9891), is obtained. The detection limit is  0.8 × 10-2 fM (S/N = 3). The average recovery for human serum detection ranged from 97.32 to 101.4% (RSD < 5%).

Fiber-optic immunosensor based on a Fabry-Perot interferometer for single-molecule detection of biomarkers.

Immunosensors capable of ultralow-concentration and single-molecule detection of biomarkers are garnering attention for the early diagnosis of cancer. Herein, a fiber-optic Fabry-Perot interferometer (FPI)-based immunosensor was used for the first time for single-molecule detection of progastrin-releasing peptide (ProGRP). The cascaded FPI structure of the immunosensor introduces a high-order harmonic Vernier effect (HVE). A piece of a side-polished D-shaped hollow-core photonic crystal fiber (HCPCF) was used as a sensing FPI, on which the biomarker was deposited to detect ProGRP. Compared with traditional FPIs with open-cavity structures, this structure provided a larger contact area and improved the sensitivity of the immunosensor. The polished side surface of the D-shaped HCPCF was modified using a gold nanoparticle-graphene oxide (AuNP@GO) nanointerface to enhance refractive index (RI) modulation via antigen-antibody binding and achieve selective energy enhancement of the binding site. The antigen binding changes the RI of the D-shaped HCPCF and the effective RI of the transmitted light in the sensing FPI, thereby changing the spectrum of the immunosensor. Experimental results showed that the high-order HVE and AuNP@GO nanointerface considerably improved the immunosensor sensitivity, exhibiting a liquid RI sensitivity of 583,000 nm/RIU. After functionalization with an anti-ProGRP antibody, the limit of detection of the immunosensor for ProGRP reached 17.1 ag/mL; moreover, the immunosensor could perform detection at the single-molecule level. The proposed novel immunosensor overcomes the sensitivity limitations of optical devices and achieves single-molecule detection of a protein.

Current situation and prospects for the clean utilization of gold tailings.

Gold tailings are characterized by low-grade, complex composition, fine embedded particle size, environmental pollution, and large land occupation. This paper describes the mineralogical properties of gold tailings, including chemical composition, phase composition, particle size distribution, and microstructure; summarizes the recycling and utilization of components such as mica, feldspar, and valuable metals in gold tailings; reviews harmless treatment measures for harmful elements in gold tailings; and adumbrated the research progress of gold tailings in the application fields of building materials, ceramics, and glass materials. Based on these discussions, a new technology roadmap that combines multistage magnetic separation and cemented filling is proposed for the clean utilization of all components of gold tailings.

Nanozyme-assisted molecularly imprinted polymer-based indirect competitive ELISA for the detection of marine biotoxin.

Saxitoxin (STX), which is produced by certain dinoflagellate species, is a type of paralytic shellfish poisoning toxin that poses a serious threat to human health and the environment. Therefore, developing a technology for the convenient and cost-effective detection of STX is imperative. In this study, we developed an affinity peptide-imprinted polymer-based indirect competitive ELISA (ic-ELISA) without using enzyme-toxin conjugates. AuNP/Co3O4@Mg/Al cLDH was synthesized by calcining AuNP/ZIF-67@Mg/Al LDH, which was obtained by combining AuNPs, ZIF-67, and flower-like Mg/Al LDH. This synthesized nanozyme exhibited high catalytic activity (Km = 0.24 mM for TMB and 132.5 mM for H2O2). The affinity peptide-imprinted polymer (MIP) was imprinted with an STX-specific template peptide (STX MIP) on a multi-well microplate and then reacted with an STX-specific signal peptide (STX SP). The interaction between the STX SP and MIP was detected using a streptavidin-coated nanozyme (SA-AuNP/Co3O4@Mg/Al cLDH). The developed MIP-based ic-ELISA exhibited excellent selectivity and sensitivity, with a limit of detection of 3.17 ng/mL (equivalent: 0.317 µg/g). Furthermore, the system was validated using a commercial ELISA kit and mussel tissue samples, and it demonstrated a high STX recovery with a low coefficient of variation. These results imply that the developed ic-ELISA can be used to detect STX in real samples.

PEI-Mediated Assembly of Fe3O4 onto SiO2-Encapsulated CsPbBr3 for Highly Sensitive Fluorescent Lateral Flow Immunoassay.

The conventional lateral flow immunoassay (LFIA) method using colloidal gold nanoparticles (Au NPs) as labeling agents faces two inherent limitations, including restricted sensitivity and poor quantitative capability, which impede early viral infection detection. Herein, we designed and synthesized CsPbBr3 perovskite quantum dot-based composite nanoparticles, CsPbBr3@SiO2@Fe3O4 (CSF), which integrated fluorescence detection and magnetic enrichment properties into LFIA technology and achieved rapid, sensitive, and convenient quantitative detection of the SARS-CoV-2 virus N protein. In this study, CsPbBr3 served as a high-quantum-yield fluorescent signaling probe, while SiO2 significantly enhanced the stability and biomodifiability of CsPbBr3. Importantly, the SiO2 shell shows relatively low absorption or scattering toward fluorescence, maintaining a quantum yield of up to 74.4% in CsPbBr3@SiO2. Assembly of Fe3O4 nanoparticles mediated by PEI further enhanced the method's sensitivity and reduced matrix interference through magnetic enrichment. Consequently, the method achieved a fluorescent detection range of 1 × 102 to 5 × 106 pg·mL-1 after magnetic enrichment, with a limit of detection (LOD) of 58.8 pg·mL-1, representing a 13.3-fold improvement compared to nonenriched samples (7.58 × 102 pg·mL-1) and a 2-orders-of-magnitude improvement over commercial colloidal gold kits. Furthermore, the method exhibited 80% positive and 100% negative detection rates in clinical samples. This approach holds promise for on-site diagnosis, home-based quantitative tests, and disease procession evaluation.

Electrochemical and Infrared Studies of a Model Bilayer of the Outer Membrane of Gram-Negative Bacteria and its Interaction with polymyxin─the Last-Resort Antibiotic.

A model bilayer of the outer membrane (OM) of Gram-negative bacteria, composed of lipid A and 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine (DMPE), was assembled on the ß-Tg modified gold (111) single crystal surface using a combination of Langmuir-Blodgett and Langmuir-Schaefer transfer. Electrochemical and spectroscopic methods were employed to study the properties of the model bilayer and its interaction with polymyxin. The model bilayer is stable on the gold surface in the transmembrane potential region between 0.0 and -0.7 V. The presence of Mg2+ coordinates with the phosphate and carboxylate groups in the leaflet of lipid A and stabilizes the structure of the model bilayer. Polymyxin causes the model bilayer leakage and damage in the transmembrane potential region between 0.2 and -0.4 V. At transmembrane potentials lower than -0.5 V, polymyxin does not affect the membrane integrity. Polymyxin binds to the phosphate and carboxylate groups in lipid A molecules and causes the increase of the tilt angle of acyl chains and the decrease of the tilt of the C═O bond. The results in this paper indicate that the antimicrobial activity of polymyxin depends on the transmembrane potential at the model bilayer and provides useful information for the development of new antibiotics.

Centrifugal Field-Flow Fractionation Enables Detection of Slight Aggregation of Nanoparticles That Impacts Their Biomedical Applications.

Nanoparticles (NPs) are anticipated to be used for various biomedical applications in which their aggregation has been an important issue. However, concerns regarding slightly aggregated but apparently monodispersed NPs have been difficult to address because of a lack of appropriate evaluation methods. Here, we report centrifugal field-flow fractionation (CF3) as a powerful method for analyzing the slight aggregation of NPs, using antibody-modified gold NPs (Ab-AuNPs) prepared by a conventional protocol with centrifugal purification as a model. While common evaluation methods such as dynamic light scattering cannot detect significant signs of aggregation, CF3 successfully detects distinct peaks of slightly aggregated NPs, including dimers and trimers. Their impact on biological interactions was also demonstrated by a cellular uptake study: slightly aggregated Ab-AuNPs exhibited 1.8 times higher cellular uptake than monodispersed Ab-AuNPs. These results suggest the importance of aggregate evaluation via CF3 as well as the need for careful attention to the bioconjugation procedures for NPs.

Hybridized quantum dot, silica, and gold nanoparticles for targeted chemo-radiotherapy in colorectal cancer theranostics.

Multimodal nanoparticles, utilizing quantum dots (QDs), mesoporous silica nanoparticles (MSNs), and gold nanoparticles (Au NPs), offer substantial potential as a smart and targeted drug delivery system for simultaneous cancer therapy and imaging. This method entails coating magnetic GZCIS/ZnS QDs with mesoporous silica, loading epirubicin into the pores, capping with Au NPs, PEGylation, and conjugating with epithelial cell adhesion molecule (EpCAM) aptamers to actively target colorectal cancer (CRC) cells. This study showcases the hybrid QD@MSN-EPI-Au-PEG-Apt nanocarriers (size ~65 nm) with comprehensive characterizations post-synthesis. In vitro studies demonstrate the selective cytotoxicity of these targeted nanocarriers towards HT-29 cells compared to CHO cells, leading to a significant reduction in HT-29 cell survival when combined with irradiation. Targeted delivery of nanocarriers in vivo is validated by enhanced anti-tumor effects with reduced side effects following chemo-radiotherapy, along with imaging in a CRC mouse model. This approach holds promise for improved CRC theranostics.

SERS biosensor with plastic antibodies for detection of a cancer biomarker protein.

Surface-enhanced Raman scattering (SERS) is a powerful method for detecting breast cancer-specific biomarkers due to its extraordinary enhancement effects obtained by localized surface plasmon resonance (LSPR) in metallic nanostructures at hotspots. In this research, gold nanostars (AuNSs) were used as SERS probes to detect a cancer biomarker at very low concentrations. To this end, we combined molecularly imprinted polymers (MIPs) as a detection layer with SERS for the detection of the biomarker CA 15-3 in point-of-care (PoC) analysis. This required two main steps: (i) the deposition of MIPs on a gold electrode, followed by a second step (ii) antibody binding with AuNSs containing a suitable Raman reporter to enhance Raman signaling (SERS). The MPan sensor was prepared by electropolymerization of the monomer aniline in the presence of CA 15-3. The template molecule was then extracted from the polymer using sodium dodecyl sulfate (SDS). In parallel, a control material was prepared in the absence of the protein (NPan). Surface modification for the control was performed using electrochemical techniques such as cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The performance of the sensor was evaluated using the SERS technique, in which the MPan sensor is first incubated with the protein and then exposed to the SERS probe. Under optimized conditions, the device showed a linear response to CA 15-3 concentrations from 0.016 to 248.51 U mL-1 in a PBS buffer at pH 7.4 in 1000-fold diluted serum. Overall, this approach demonstrates the potential of SERS as an optical reader and opens a new avenue for biosensing applications.

Evaluation of Lippia scaberrima Sond. and Aspalathus linearis (Burm.f.) R. Dahlgren extracts on human CYP enzymes and gold nanoparticle synthesis: implications for drug metabolism and cytotoxicity.

BACKGROUND: Metabolism is an important component of the kinetic characteristics of herbal constituents, and it often determines the internal dose and concentration of these effective constituents at the target site. The metabolic profile of plant extracts and pure compounds need to be determined for any possible herb-drug metabolic interactions that might occur. METHODS: Various concentrations of the essential oil of Lippia scaberrima, the ethanolic extract of Lippia scaberrima alone and their combinations with fermented and unfermented Aspalathus linearis extract were used to determine the inhibitory potential on placental, microsomal and recombinant human hepatic Cytochrome P450 enzymes. Furthermore, the study investigated the synthesis and characterization of gold nanoparticles from the ethanolic extract of Lippia scaberrima as a lead sample. Confirmation and characterization of the synthesized gold nanoparticles were conducted through various methods. Additionally, the cytotoxic properties of the ethanolic extract of Lippia scaberrima were compared with the gold nanoparticles synthesized from Lippia scaberrima using gum arabic as a capping agent. RESULTS: All the samples showed varying levels of CYP inhibition. The most potent inhibition took place for CYP2C19 and CYP1B1 with 50% inhibitory concentration (IC50) values of less than 0.05 µg/L for the essential oil tested and IC50-values between 0.05 µg/L-1 µg/L for all the other combinations and extracts tested, respectively. For both CYP1A2 and CYP2D6 the IC50-values for the essential oil, the extracts and combinations were found in the range of 1 - 10 µg/L. The majority of the IC50 values found were higher than 10 µg/L and, therefore, were found to have no inhibition against the CYP enzymes tested. CONCLUSION: Therefore, the essential oil of Lippia scaberrima, the ethanolic extract of Lippia scaberrima alone and their combinations with Aspalathus linearis do not possess any clinically significant CYP interaction potential and may be further investigated for their adjuvant potential for use in the tuberculosis treatment regimen. Furthermore, it was shown that the cytotoxic potential of the Lippia scaberrima gold nanoparticles was reduced by twofold when compared to the ethanolic extract of Lippia scaberrima.

A dual-mode fluorometric/colorimetric sensor for sulfadimethoxine detection based on Prussian blue nanoparticles and carbon dots.

A dual-mode (colorimetric/fluorescence) nanoenzyme-linked immunosorbent assay (NLISA) was developed based on Au-Cu nanocubes generating Prussian blue nanoparticles (PBNPs). It is expected that this method can be used to detect the residues of sulfonamides in the field, and solve the problem of long analysis time and high cost of the traditional method. Sulfadimethoxine (SDM) was selected as the proof-of-concept target analyte. The Au-Cu nanocubes were linked to the aptamer by amide interaction, and the Au-Cu nanocubes, SDM and antibody were immobilized on a 96-well plate using the sandwich method. The assay generates PBNPs by oxidising the Cu shells on the Au-Cu nanocubes in the presence of hydrochloric acid, Fe3+ and K3[Fe (CN)6]. In this process, the copper shell undergoes oxidation to Cu2+ and subsequently Cu2 + further quenches the fluorescence of the carbon point. PBNPs exhibit peroxidase-like activity, oxidising 3,3',5,5'-tetramethylbenzidine (TMB) to OX-TMB in the presence of H2O2, which alters the colorimetric signal. The dual-mode signals are directly proportional to the sulfadimethoxine concentration within the range 10- 3~10- 7 mg/mL. The limit of detection (LOD) of the assay is 0.023 ng/mL and 0.071 ng/mL for the fluorescent signal and the colorimetric signal, respectively. Moreover, the assay was successfully applied to determine sulfadimethoxine in silver carp, shrimp, and lamb samples with satisfactory results.

Detection of P. malariae using a new rapid isothermal amplification lateral flow assay.

BACKGROUND: While Plasmodium falciparum and Plasmodium vivax cause the majority of malaria cases and deaths, infection by Plasmodium malariae and other Plasmodium species also causes morbidity and mortality. Current understanding of these infections is limited in part by existing point-of-care diagnostics that fail to differentiate them and have poor sensitivity for low-density infections. Accurate diagnosis currently requires molecular assays performed in well-resourced laboratories. This report describes the development of a P. malariae diagnostic assay that uses rapid, isothermal recombinase polymerase amplification (RPA) and lateral-flow-strip detection. METHODS: Multiple combinations of custom RPA primers and probes were designed using publicly available P. malariae genomic sequences, and by modifying published primer sets. Based on manufacturer RPA reaction conditions (TwistDx nfo kit), an isothermal assay was optimized targeting the multicopy P. malariae 18S rRNA gene with 39 °C incubation and 30-min run time. RPA product was visualized using lateral strips (FAM-labeled, biotinylated amplicon detected by a sandwich immunoassay, visualized using gold nanoparticles). Analytical sensitivity was evaluated using 18S rRNA plasmid DNA, and clinical sensitivity determined using qPCR-confirmed samples collected from Tanzania, Ethiopia, and the Democratic Republic of the Congo. RESULTS: Using 18S rRNA plasmid DNA, the assay demonstrates a detection limit of 10 copies/µL (~ 1.7 genome equivalents) and 100% analytical specificity. Testing in field samples showed 95% clinical sensitivity and 88% specificity compared to qPCR. Total assay time was less than 40 min. CONCLUSION: Combined with simplified DNA extraction methods, the assay has potential for future field-deployable, point-of-care use to detect P. malariae infection, which remains largely undiagnosed but a neglected cause of chronic malaria. The assay provides a rapid, simple readout on a lateral flow strip without the need for expensive laboratory equipment.

Molecular Weights of Polyethyleneimine-Dependent Physicochemical Tuning of Gold Nanoparticles and FRET-Based Turn-On Sensing of Polymyxin B.

Environmental monitoring and the detection of antibiotic contaminants require expensive and time-consuming techniques. To overcome these challenges, gold nanoparticle-mediated fluorometric "turn-on" detection of Polymyxin B (PMB) in an aqueous medium was undertaken. The molecular weight of polyethyleneimine (PEI)-dependent physicochemical tuning of gold nanoparticles (PEI@AuNPs) was achieved and employed for the same. The three variable molecular weights of branched polyethyleneimine (MW 750, 60, and 1.3 kDa) molecules controlled the nano-geometry of the gold nanoparticles along with enhanced stabilization at room temperature. The synthesized gold nanoparticles were characterized through various advanced techniques. The results revealed that polyethyleneimine-stabilized gold nanoparticles (PEI@AuNP-1-3) were 4.5, 7.0, and 52.5 nm in size with spherical shapes, and the zeta potential values were 29.9, 22.5, and 16.6 mV, respectively. Accordingly, the PEI@AuNPs probes demonstrated high sensitivity and selectivity, with a linear relationship curve over a concentration range of 1-6 µM for polymyxin B. The limit of detection (LOD) was calculated as 8.5 nM. This is the first unique report of gold nanoparticle nano-geometry-dependent FRET-based turn-on detection of PMB in an aqueous medium. We believe that this approach would offer a complementary strategy for the development of a highly sophisticated and advanced sensing system for PMB and act as a template for the development of new nanomaterial-based engineered sensors for rapid antibiotic detection in environmental as well as biological samples.

Energy Transfer-Based Recognition of Membrane Cholesterol by Controlling Intradistance of Linker.

Gold nanoparticles (AuNPs) are good candidates for donor material in energy transfer systems and can easily be functionalized with various ligands on the surface with Au-S bonding. Cyclodextrin (CD) forms inclusion complexes with fluorophores due to its unique structure for host-guest interaction. In this study, we fabricated ßCD-functionalized AuNPs using different lengths of thiol ligands and recognized cholesterol to confirm the energy-transfer-based turn-on fluorescence mechanism. AuNP-ßCD conjugated with various thiol ligands and quenched the fluorescein (Fl) dye, forming ßCD-Fl inclusion complexes. As the distance between AuNPs and ßCD decreased, the quenching efficiency became higher. The quenched fluorescence was recovered when the cholesterol replaced the Fl because of the stronger binding affinity of the cholesterol with ßCD. The efficiency of cholesterol recognition was also affected by the energy transfer effect because the shorter ßCD ligand had a higher fluorescence recovery. Furthermore, we fabricated a liposome with cholesterol embedded in the lipid bilayer membrane to mimic the cholesterol coexisting with lipids in human serum. These cellular cholesterols accelerated the replacement of the Fl molecules, resulting in a fluorescence recovery higher than that of pure lipid. These discoveries are expected to give guidance towards cholesterol sensors or energy-transfer-based biosensors using AuNPs.