A novel integrated lateral flow immunoassay platform for the detection of cardiac troponin I using hierarchical dendritic copper-nickel nanostructures

Cardiac troponin I (cTnI) is a critical biomarker for the diagnosis of acute myocardial infarction (AMI). Herein, we report a novel integrated lateral flow immunoassay (LFIA) platform for highly sensitive point-of-care testing (POCT) of cTnI using hierarchical dendritic copper-nickel (HD-nanoCu-Ni) nanostructures. The electrodeposited HD-nanoCu-Ni film (∼22 μm thick) on an ITO-coated glass substrate exhibits superior capillary action and structural integrity. These properties enable efficient sample transport and antibody immobilization, making it a compelling alternative to conventional multi-component paper-based LFIA test strips, which are often plagued by structural fragility and susceptibility to moisture damage. The biofunctionalized HD-nanoCu-Ni substrates were laser-etched with lateral flow channels, including a sample loading/conjugate release zone, a test zone, and a control zone. Numerical simulations were used to further optimize the design of these channels to achieve optimal fluid flow and target capture. The HD-nanoCu-Ni LFIA device utilizes a fluorescence quenching based sandwich immunoassay format using antibody-labeled gold nanoparticles (AuNPs) as quenchers. Two different fluorescent materials, fluorescein isothiocyanate (FITC) and CdSe@ZnS quantum dots (QDs), were used as background fluorophores in the device. Upon the formation of a sandwich immunocomplex with cTnI on the HD-nanoCu-Ni device, introduced AuNPs led to the fluorescence quenching of the background fluorophores. The total assay time was approximately 15 min, demonstrating the rapid and efficient nature of the HD-nanoCu-Ni LFIA platform. For FITC, both inner filter effect (IFE) and fluorescence resonance energy transfer (FRET) contributed to the AuNP-mediated quenching. In the case of CdSe@ZnS QDs, IFE dominated the AuNP-induced quenching. Calibration curves were established based on the relationship between the fluorescence quenching intensity and cTnI concentration in human serum samples, ranging from 0.5 to 128 ng/mL. The limits of detection (LODs) were determined to be 0.27 ng/mL and 0.40 ng/mL for FITC and CdSe@ZnS QDs, respectively. A method comparison study using Passing-Bablok regression analysis on varying cTnI concentrations in human serum samples confirmed the equivalence of the HD-nanoCu-Ni LFIA platform to a commercial fluorescence cTnI LFIA assay kit, with no significant systematic or proportional bias observed.

Nanogold-based materials in medicine: from their origins to their future

The properties of gold-based materials have been explored for centuries in several research fields, including medicine. Multiple published production methods for gold nanoparticles (AuNPs) have shown that the physicochemical and optical properties of AuNPs depend on the production method used. These different AuNP properties have allowed exploration of their usefulness in countless distinct biomedical applications over the last few years. Here we present an extensive overview of the most commonly used AuNP production methods, the resulting distinct properties of the AuNPs and the potential application of these AuNPs in diagnostic and therapeutic approaches in biomedicine.

Fluorescence resonance energy transfer-thermal lens spectrometry (FRET-TLS) as molecular counting of methamphetamine

A novel and sensitive approach has been presented for the determination of methamphetamine (METH) based on fluorescence resonance energy transfer-thermal lens spectrometry (FRET-TLS). Due to the affinity of fluorescein molecules to the surface of AuNPs through the electrostatic interaction and thereby caused reduction of the distance between fluorescein and AuNPs, the best way for de-excitation of excited fluorescein is FRET. The energy absorbed by fluorescein transferred to AuNPs causes enhancement of the thermal lens effect. The thermal lens of the fluorescence molecule could be enhanced through a proper acceptor. Upon the addition of methamphetamine, the fluorescein molecules are detached from the surface of AuNPs, due to the stronger adsorption of methamphetamine. As a result, the fluorescence of fluorescein recovered, and the thermal lens effect of fluorescein decreased. The mechanism of energy transfer was evaluated by two different methods including time-resolved spectroscopy and thermal lens spectrometry. Under the optimal conditions, the thermal lens signal was linearly proportional to methamphetamine concentration in the range 5 - 80 nM. The limit of detection and limit of quantitation were 1.5 nM and 4.5 nM, respectively. The detection volume and limit of molecules in the detection volume were 960 attoliter and 87 molecules, respectively. The method was successfully applied for the determination of methamphetamine in human blood plasma and urine.

Recent Trends in Noble Metal Nanoparticles for Colorimetric Chemical Sensing and Micro-Electronic Packaging Applications

Noble metal NPs are highly attractive candidates because of their unique combination of physical, chemical, mechanical, and structural properties. A lot of developments in this area are still fascinating the materials research community, and are broadly categorized in various sectors such as chemical sensors, biosensors, Förster resonance energy transfer (FRET), and microelectronic applications. The related function and properties of the noble metals in these areas can be further tailored by tuning their chemical, optical, and electronic properties that are influenced by their size, shape, and distribution. The most widely used Au and Ag NPs in dispersed phase below 100 nm exhibit strong color change in the visible range which alters upon aggregation of the NPs. The chemical sensing of the analyte is influenced by these NPs aggregates. In this article, we have summarized the uniqueness of noble metal NPs, their synthesis methods, nucleation and growth process, and their important applications in chemical sensing, microelectronic packaging, and Förster resonance energy transfer.

Establishment of an Indirect Competitive Enzyme-Linked Immunosorbent Method for the Detection of Heavy Metal Cadmium in Food Packaging Materials

Heavy metals in food packaging materials have been indicated to release into the environment at slow rates. Heavy metal contamination, especially that of cadmium (Cd), is widely acknowledged as a global environment threat that leads to continuous growing pollution levels in the environment. Traditionally, the detection of the concentration of Cd relies on expensive precision instruments, such as inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma-atomic emission spectrometry (ICP-AES). In this study, an indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) based on a specific monoclonal antibody was proposed to rapidly detect Cd. The half-inhibitory concentration and detection sensitivity of the anti-cadmium monoclonal antibody of the ic-ELISA were 5.53 ng mL-1 and 0.35 ng mL-1, respectively. The anti-Cd monoclonal antibody possessed high specificity while diagnosising other heavy metal ions, including Al (III), Ca (II), Cu (II), Fe (III), Hg (II), Mg (II), Mn (II), Pb (II), Zn (II), Cr (III) and Ni (II). The average recovery rates of Cd ranged from 89.03-95.81% in the spiked samples of packing materials, with intra- and inter-board variation coefficients of 7.20% and 6.74%, respectively. The ic-ELISA for Cd detection was applied on 72 food packaging samples that consisted of three material categories-ceramic, glass and paper. Comparison of the detection results with ICP-AES verified the accuracy of the ic-ELISA. The correlation coefficient between the ic-ELISA and the ICP-AES methods was 0.9634, demonstrating that the proposed ic-ELISA approach could be a useful and effective tool for the rapid detection of Cd in food packaging materials.

Thermo-responsive polymer encapsulated gold nanorods for single continuous wave laser-induced photodynamic/photothermal tumour therapy

Owing to strong and tunable surface plasmon resonance (SPR) effect and good biocompatibility, gold nanoparticles have been suggested to be a versatile platform for a broad range of biomedical applications. In this study, a new nanoplatform of thermo-responsive polymer encapsulated gold nanorods incorporating indocyanine green (ICG) was designed to couple the photothermal properties of gold nanorods (AuNRs) and the photodynamic properties of ICG to enhance the photodynamic/photothermal combination therapy (PDT/PTT). In addition to the significantly increased payload and enhancing photostability of ICG, the polymer shell in the nanoplatform also has thermo-responsive characteristics that can control the release of drugs at tumour sites upon the laser irradiation. On the basis of these improvements, the nanoplatform strongly increased drug aggregation at the tumour site and improved the photothermal/photodynamic therapeutic efficacy. These results suggest that this nanoplatform would be a great potential system for tumour imaging and antitumour therapy.

Homogeneous Quenching Immunoassay for Fumonisin B1 Based on Gold Nanoparticles and an Epitope-Mimicking Yellow Fluorescent Protein

Homogeneous immunoassays represent an attractive alternative to traditional heterogeneous assays due to their simplicity, sensitivity, and speed. On the basis of a previously identified epitope-mimicking peptide, or mimotope, we developed a homogeneous fluorescence quenching immunoassay based on gold nanoparticles (AuNPs) and a recombinant epitope-mimicking fusion protein for the detection of mycotoxin fumonisin B₁ (FB₁). The fumonisin mimotope was cloned as a fusion protein with a yellow fluorescent protein that could be used directly as the tracer for FB₁ detection without the need of labeling or a secondary antibody. Furthermore, owing to the fluorescence quenching ability of AuNPs, a homogeneous immunoassay could be performed in a single step without washing steps to separate the unbound tracer. The homogeneous quenching assay showed negligible matrix effects in 5% wheat extract and high sensitivity for FB₁ detection, with a dynamic range from 7.3 to 22.6 ng mL^-1, a detection limit of 1.1 ng mL^-1, and IC₅₀ value of 12.9 ng mL^-1, which was significantly lower than the IC₅₀ value of the previously reported assay using the synthetic counterpart of the same mimotope in a microarray format. The homogeneous assay was demonstrated to be specific for fumonisins B₁ and B₂, as no significant cross-reactivity with other mycotoxins was observed, and acceptable recoveries (86% for FB₁ 2000 μg kg^-1 and 103% for FB₁ 4000 μg kg^-1), with relative standard deviation less than 6.5%, were reported from spiked wheat samples, proving that the method could provide a valuable tool for simple analysis of mycotoxin-contaminated food samples.

Highly sensitive and visual detection of guanosine 3'-diphosphate-5'-di(tri)phosphate (ppGpp) in bacteria based on copper ions-mediated 4-mercaptobenzoic acid modified gold nanoparticles

Guanosine 3'-diphosphate-5'-di(tri)phosphate (ppGpp) plays a crucial role in the gene expression, metabolism, growth, and other significant processes of microorganisms. In this work, a facile sensitive and visual strategy for the detection of ppGpp has been established by developing a colorimetric probe of copper ions (Cu²⁺)-mediated 4-mercaptobenzoic acid (4-MBA) modified gold nanoparticles (AuNPs). The sensing process was characterized by transmission electron microscopy (TEM), zeta potential, dynamic light scattering (DLS) and UV-vis spectroscopy. The strategy not only achieves desirable performance over a wide concentration range (0.05-10 μM), but also exhibits excellent selectivity over other nucleotides and biomolecules. In addition, the results could be visualized by the naked eye. We have demonstrated the determination of ppGpp in Bacillus subtilis lysate samples.

Gold nanoparticle-catalyzed uranine reduction for signal amplification in fluorescent assays for melamine and aflatoxin B1

A multifunctional fluorescence platform has been constructed based on gold nanoparticle (AuNP)-catalyzed uranine reduction. The catalytic reduction of uranine was conducted in aqueous solution using AuNPs as nanocatalyst and sodium borohydride as reducing reagent, which was monitored by fluorescence and UV-vis spectroscopy. The reaction rate was highly dependent on the concentration, size and dispersion state of AuNPs. When AuNPs aggregated, their catalytic ability decreased, and thereby a label-free fluorescent assay was developed for the detection of melamine, which can be used for melamine determination in milk. In addition, a fluorescent immunoassay for aflatoxin B1 (AFB1) was established using the catalytic reaction for signal amplification based on target-induced concentration change of AuNPs, where AFB1-BSA-coated magnetic beads and anti-AFB1 antibody-conjugated AuNPs were employed as capture and signal probe, respectively. The detection can be accomplished in 1 h and acceptable recoveries in spiked maize samples were achieved. The developed fluorescence system is simple, sensitive and specific, which could be used for the detection of a wide range of analytes.

Applications of Hairpin DNA-Functionalized Gold Nanoparticles for Imaging mRNA in Living Cells

Molecular imaging agents are useful for imaging molecular processes in living systems in order to elucidate the function of molecular mediators in health and disease. Here, we demonstrate a technique for the synthesis, characterization, and application of hairpin DNA-functionalized gold nanoparticles (hAuNPs) as fluorescent hybridization probes for imaging mRNA expression and spatiotemporal dynamics in living cells. These imaging probes feature gold colloids linked to fluorophores via engineered oligonucleotides to resemble a molecular beacon in which the gold colloid serves as the fluorescence quencher in a fluorescence resonance energy transfer system. Target-specific hybridization of the hairpin oligonucleotide enables fluorescence de-quenching and subsequent emission with high signal to noise ratios. hAuNPs exhibit high specificity without adverse toxicity or the need for transfection reagents. Furthermore, tunability of hAuNP emission profiles by selection of spectrally distinct fluorophores enables multiplexed mRNA imaging applications. Therefore, hAuNPs are promising tools for imaging gene expression in living cells. As a representative application of this technology, we discuss the design and applications of hAuNP targeted against distinct matrix metalloproteinase enzymes for the multiplexed detection of mRNA expression in live breast cancer cells using flow cytometry and fluorescence microscopy.

Charge Transfer at Hybrid Interfaces: Plasmonics of Aromatic Thiol-Capped Gold Nanoparticles

Although gold nanoparticles stabilized by organic thiols are the building blocks in a wide range of applications, the role of the ligands on the plasmon resonance of the metal core has been mostly ignored until now. Herein, a methodology based on the combination of spectroscopic ellipsometry and UV-vis spectroscopy is applied to extract dielectric functions of the different components. It is shown that aromatic thiols allow a significant charge transfer at the hybrid interface with the s and d bands of the gold core that yields "giant" red shifts of the plasmon band, up to 40 nm for spherical particles in the size range of 3-5 nm. These results suggest that hybrid nanoplasmonic devices may be designed through the suitable choice of metal core and organic components for optimized charge exchange.

Carboxy-terminated immuno-SERS tags overcome non-specific aggregation for the robust detection and localization of organic media in artworks

Surface-enhanced Raman scattering (SERS) nano-tags with a carboxy-terminated PEG surface coating overcome non-specific aggregation when applied for the immunological detection and localization of proteinaceous binding media in art samples.

Nanoparticle based fluorescence resonance energy transfer (FRET) for biosensing applications

Nanoparticle based FRET assays have higher energy transfer efficiency and better performance compared with traditional organic fluorophore based FRET assays.

Probing disease-related proteins with fluorogenic composite materials

Construction of composite materials based on the self-assembly of fluorescently labeled biomolecules with a variety of micro- or nano-quenching materials (by the Förster Resonance Energy Transfer mechanism) for the fluorogenic recognition of disease-related proteins has become a dynamic research topic in the field of fluorescence recognition. Here we summarize the recent progress on the composition of fluorescence dye-labeled biomolecules including sugars, peptides and nucleotides with organic (graphene and carbon nanotubes) and inorganic (gold nanoparticles) materials. Their application in the fluorescence detection of proteins and enzymes on both the molecular and cellular levels is discussed. Perspectives are proposed with respect to the future directions of employing these composite materials in the recognition of pathological proteins.

Nanomaterials for ultrasensitive protein detection

The advances of nanomaterials have provided exciting technologies and novel materials for protein detection, based on the unique properties associated with nanoscale phenomena such as plasmon resonance, catalysis and energy transfer. This article reviews a series of nanomaterials including nanoparticles, nanofibers, nanowires, and nanosheets, and evaluates their performances in the application for protein detection, focusing on approaches that realize ultrasensitive detection. Many of these nanomaterials were used to analyze clinically relevant protein biomarkers. Their detection in the picomolar, femtomolar or even zeptomolar regime has been realized, sometimes even with naked-eye readout. We summarize the detection methods and results according to materials and targets, review the current challenges, and discuss the solution in the context of technological integration such as combining nanomaterials with microfluidics, and classical analytical technologies.