Rapid single-step upconversion-linked immunosorbent assay for diclofenac

Nanoparticle-Based Bioaffinity Assays: From the Research Laboratory to the Market

Advances in the development of new biorecognition elements, nanoparticle-based labels as well as instrumentation have inspired the design of new bioaffinity assays. This review critically discusses the potential of nanoparticles to replace current enzymatic or molecular labels in immunoassays and other bioaffinity assays. Successful implementations of nanoparticles in commercial assays and the need for rapid tests incorporating nanoparticles in different roles such as capture support, signal generation elements, and signal amplification systems are highlighted. The limited number of nanoparticles applied in current commercial assays can be explained by challenges associated with the analysis of real samples (e.g., blood, urine, or nasal swabs) that are difficult to resolve, particularly if the same performance can be achieved more easily by conventional labels. Lateral flow assays that are based on the visual detection of the red-colored line formed by colloidal gold are a notable exception, exemplified by SARS-CoV-2 rapid antigen tests that have moved from initial laboratory testing to widespread market adaption in less than two years.

Artificial Intelligence-Aided Massively Parallel Spectroscopy of Freely Diffusing Nanoscale Entities

Massively parallel spectroscopy (MPS) of many single nanoparticles in an aqueous dispersion is reported. As a model system, bioconjugated photon-upconversion nanoparticles (UCNPs) with a near-infrared excitation are prepared. The UCNPs are doped either with Tm3+ (emission 450 and 802 nm) or Er3+ (emission 554 and 660 nm). These UCNPs are conjugated to biotinylated bovine serum albumin (Tm3+-doped) or streptavidin (Er3+-doped). MPS is correlated with an ensemble spectra measurement, and the limit of detection (1.6 fmol L-1) and the linearity range (4.8 fmol L-1 to 40 pmol L-1) for bioconjugated UCNPs are estimated. MPS is used for observing the bioaffinity clustering of bioconjugated UCNPs. This observation is correlated with a native electrophoresis and bioaffinity assay on a microtiter plate. A competitive MPS bioaffinity assay for biotin is developed and characterized with a limit of detection of 6.6 nmol L-1. MPS from complex biological matrices (cell cultivation medium) is performed without increasing background. The compatibility with polydimethylsiloxane microfluidics is proven by recording MPS from a 30 μm deep microfluidic channel.

Revisiting carboxylic group functionalization of silica sol-gel materials

The carboxylic chemical group is a ubiquitous moiety present in amino acids, a ligand for transition metals, a colloidal stabilizer, and a weak acidic ion-exchanger in polymeric resins and given this property, it is attractive for responsive materials or nanopore-based gating applications. As the number of uses increases, subtle requirements are imposed on this molecular group when anchored to various platforms for the functioning of an integrated chemical system. In this context, silica stands as an inert and multipurpose platform that enables the anchoring of multiple chemical entities combined through several orthogonal synthesis methods on the interface. Surface chemical modification relies on the use of organoalkoxysilanes that must meet the demand of tuned chemical properties; this, in turn, urges for innovative approaches for having an improved, but simple, organic toolbox. Starting from commonly available molecular precursors, several approaches have emerged: hydrosilylation, click thiol-ene additions, the use of carbodiimides or the reaction between cyclic anhydrides and anchored amines. In this review, we analyze the importance of the COOH groups in the area of materials science and the commercial availability of COOH-based silanes and present new approaches for obtaining COOH-based organoalkoxide precursors. Undoubtedly, this will attract widespread interest for the ultimate design of highly integrated chemical platforms.

Immunoaffinity extraction followed by enzymatic digestion for the isolation and identification of proteins employing automated μSPE reactors and mass spectrometry

This work describes a novel automated and rapid method for bottom-up proteomics combining protein isolation with a micro-immobilised enzyme reactor (IMER). Crosslinking chemistry based on 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide/N-hydroxysuccinimide (EDC/NHS) coupling was exploited to immobilise trypsin and antibodies onto customisable silica particles coated with carboxymethylated dextran (CMD). This novel silica–CMD solid-phase extraction material was characterised using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), conductometric titrations and enzymatic colorimetric assays. Micro-solid-phase extraction (μSPE) cartridges equipped with the modified CMD material were employed and integrated into an automated and repeatable workflow using a sample preparation workstation to achieve rapid and repeatable protein isolation and pre-concentration, followed by tryptic digestion producing peptide fragments that were identified by liquid chromatography mass spectrometry (LC-MS).

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PMVEMA-coated upconverting nanoparticles for upconversion-linked immunoassay of cardiac troponin

Surface engineering of upconverting nanoparticles (UCNPs) is crucial for their bioanalytical applications. Here, an antibody specific to cardiac troponin I (cTnI), an important biomarker for acute myocardial infection, was covalently immobilized on the surface of UCNPs to prepare a label for the detection of cTnI biomarker in an upconversion-linked immunoassay (ULISA). Core-shell UCNPs (NaYF₄:Yb,Tm@NaYF₄) were first coated with poly(methyl vinyl ether-alt-maleic acid) (PMVEMA) and then conjugated to antibodies. The morphology (size and uniformity), hydrodynamic diameter, chemical composition, and amount of coating on the of UCNPs, as well as their upconversion luminescence, colloidal stability, and leaching of Y³⁺ ions into the surrounding media, were determined. The developed ULISA allowed reaching a limit of detection (LOD) of 0.13 ng/ml and 0.25 ng/ml of cTnI in plasma and serum, respectively, which represents 12- and 2-fold improvement to conventional enzyme-linked immunosorbent based on the same immunoreagents.

Bioconjugates of photon-upconversion nanoparticles for cancer biomarker detection and imaging

The detection of cancer biomarkers in histological samples and blood is of paramount importance for clinical diagnosis. Current methods are limited in terms of sensitivity, hindering early detection of disease. We have overcome the shortcomings of currently available staining and fluorescence labeling methods by taking an integrative approach to establish photon-upconversion nanoparticles (UCNP) as a powerful platform for cancer detection. These nanoparticles are readily synthesized in different sizes to yield efficient and tunable short-wavelength light emission under near-infrared excitation, which eliminates optical background interference of the specimen. Here we present a protocol for the synthesis of UCNPs by high-temperature co-precipitation or seed-mediated growth by thermal decomposition, surface modification by silica or poly(ethylene glycol) that renders the particles resistant to nonspecific binding, and the conjugation of streptavidin or antibodies for biological detection. To detect blood-based biomarkers, we present an upconversion-linked immunosorbent assay for the analog and digital detection of the cancer marker prostate-specific antigen. When applied to immunocytochemistry analysis, UCNPs enable the detection of the breast cancer marker human epidermal growth factor receptor 2 with a signal-to-background ratio 50-fold higher than conventional fluorescent labels. UCNP synthesis takes 4.5 d, the preparation of the antibody-silica-UCNP conjugate takes 3 d, the streptavidin-poly(ethylene glycol)-UCNP conjugate takes 2-3 weeks, upconversion-linked immunosorbent assay takes 2-4 d and immunocytochemistry takes 8-10 h. The procedures can be performed after standard laboratory training in nanomaterials research.

Application of up-conversion molecularly imprinted nanoprobe for selective recognition and straightforward detection of 4-aminobiphenyl

A new method was developed for selectively and rapidly detecting carcinogen 4-aminobiphenyl, with lower limit of detection and wider linear range. Up-conversion nanoparticles β-NaGdF₄:Yb³⁺, Er³⁺ was the first time to choose as light-emitting signal component. Molecularly imprinted polymers (MIPs) with specific recognition ability were successfully coated on the surface of β-NaGdF₄:Yb³⁺, Er³⁺ to obtain a nano fluorescent probe for detecting 4-aminobiphenyl. The effect of addition amount of β-NaGdF₄:Yb³⁺, Er³⁺ on the detection ability of β-NaGdF₄:Yb³⁺, Er³⁺@MIPs was studied, and composite fluorescence nanoprobe with the best performance was obtained. β-NaGdF₄:Yb³⁺, Er³⁺@MIPs were characterized by transmission electron microscopy, X-ray powder diffractometer, Fourier transform infrared spectroscopy and thermogravimetric analysis. The fluorescence intensity of β-NaGdF₄:Yb³⁺, Er³⁺@MIPs decreased significantly compared with molecularly non-imprinted polymers β-NaGdF₄:Yb³⁺, Er³⁺@NIPs (the maximum emission peak is at 541 nm) in the presence of 4-aminobiphenyl. Adsorption isotherm and adsorption kinetics between UCNP@MIPs and 4-ABP have been investigated and a satisfactory imprinting factor is 2.5. The detection mechanism is proved to be based on Langmuir adsorption and internal filtration effect. Under optimal experimental conditions, the limit of detection and quantification are 0.16 μM and 0.53 μM, respectively. The linear range of response is 1-50 μM, and RSD is less than 6.7%. This method was applied to determining river water samples in order to evaluate the practicability, and the good recovery rate is between 98.89% and 109.7%. These evidences demonstrate that β-NaGdF₄:Yb³⁺, Er³⁺@MIPs is successfully used for the detection of 4-aminobiphenyl.

A rapid magnetic bead-based immunoassay for sensitive determination of diclofenac

Increasing contamination of environmental waters with pharmaceuticals represents an emerging threat for the drinking water quality and safety. In this regard, fast and reliable analytical methods are required to allow quick countermeasures in case of contamination. Here, we report the development of a magnetic bead-based immunoassay (MBBA) for the fast and cost-effective determination of the analgesic diclofenac (DCF) in water samples, based on diclofenac-coupled magnetic beads and a robust monoclonal anti-DCF antibody. A novel synthetic strategy for preparation of the beads resulted in an assay that enabled for the determination of diclofenac with a significantly lower limit of detection (400 ng/L) than the respective enzyme-linked immunosorbent assay (ELISA). With shorter incubation times and only one manual washing step required, the assay demands for remarkably shorter time to result (< 45 min) and less equipment than ELISA. Evaluation of assay precision and accuracy with a series of spiked water samples yielded results with low to moderate intra- and inter-assay variations and in good agreement with LC–MS/MS reference analysis. The assay principle can be transferred to other, e.g., microfluidic, formats, as well as applied to other analytes and may replace ELISA as the standard immunochemical method.

Design and Analytical Performances of a Diclofenac Biosensor for Water Resources Monitoring

Because the broadly consumed pain killer diclofenac (DCF) is a recognized pollutant, monitoring of its concentration is routinely performed in surface waters. As a valuable alternative to chromatographic and immunochemical assays, we developed a piezoelectric immunosensor to quantify DCF, first in buffer (PBS) and then in river water samples. A sensing layer comprising DCF was built up on the surface of silica-coated quartz sensors using a robust coupling chemistry. Binding of a highly affine monoclonal anti-DCF antibody was monitored in real time by quartz crystal microbalance with dissipation (QCM-D) measurements from which were determined a dissociation constant K_D of 0.24 nM and an acoustic antibody surface coverage of 1120 ng/cm² at saturation. On the other hand, an optical antibody surface coverage of 260 ng/cm² was determined by combined nanoplasmonic sensing measurement, giving a hydration percentage of 75% for the antibody monolayer. DCF assay was further set up following a competitive format for which binding of antibody to the sensing layer is inhibited by DCF in solution. The piezoelectric sensor response expressed as frequency shift ΔF was inversely related to the concentration of DCF with a dynamic range of 15-46 nM and a limit of detection (LoD) of 9.5 nM (2.8 μg/L) in PBS. This piezoelectric immunosensor was eventually applied to the assay of DCF in surface water samples taken at three different locations in the Seine and Marne rivers. The calculated concentration of DCF in these samples was in good agreement with official data published by the French center of water analysis eaufrance.

Photoluminescent Nanoparticles for Chemical and Biological Analysis and Imaging

Research related to the development and application of luminescent nanoparticles (LNPs) for chemical and biological analysis and imaging is flourishing. Novel materials and new applications continue to be reported after two decades of research. This review provides a comprehensive and heuristic overview of this field. It is targeted to both newcomers and experts who are interested in a critical assessment of LNP materials, their properties, strengths and weaknesses, and prospective applications. Numerous LNP materials are cataloged by fundamental descriptions of their chemical identities and physical morphology, quantitative photoluminescence (PL) properties, PL mechanisms, and surface chemistry. These materials include various semiconductor quantum dots, carbon nanotubes, graphene derivatives, carbon dots, nanodiamonds, luminescent metal nanoclusters, lanthanide-doped upconversion nanoparticles and downshifting nanoparticles, triplet-triplet annihilation nanoparticles, persistent-luminescence nanoparticles, conjugated polymer nanoparticles and semiconducting polymer dots, multi-nanoparticle assemblies, and doped and labeled nanoparticles, including but not limited to those based on polymers and silica. As an exercise in the critical assessment of LNP properties, these materials are ranked by several application-related functional criteria. Additional sections highlight recent examples of advances in chemical and biological analysis, point-of-care diagnostics, and cellular, tissue, and in vivo imaging and theranostics. These examples are drawn from the recent literature and organized by both LNP material and the particular properties that are leveraged to an advantage. Finally, a perspective on what comes next for the field is offered.

Antibody conjugation to carboxyl-modified microspheres through N-hydroxysuccinimide chemistry for automated immunoassay applications: A general procedure

Immunochemical techniques are the workhorse for sample enrichment and detection of a large variety of analytes. In contrast to classical microtiter plate-based assays, microparticles are a next generation solid support, as they promote automation of immunoassays using flow-based techniques. Antibody immobilization is a crucial step, as these reagents are expensive, and inefficient coupling can result in low sensitivities. This paper proposes a general procedure for efficient immobilization of antibodies onto TentaGel particles, via N-hydroxysuccinimide chemistry. The goal was the preparation of solid supports with optimum immunorecognition, while increasing the sustainability of the process. The influence of buffer composition, activation and coupling time, as well as the amount of antibody on the immobilization efficiency was investigated, resorting to fluorophore-labeled proteins and fluorescence imaging. Buffer pH and activation time are the most important parameters for efficient coupling. It is demonstrated, that the hydrolysis of N-hydroxysuccinimide esters occurs at similar rates as in solution, limiting the utilizable time for coupling. Finally, applicability of the generated material for automated affinity extraction is demonstrated on the mesofluidic platform lab-on-valve.

The effects of photon-upconversion nanoparticles on the growth of radish and duckweed: Bioaccumulation, imaging, and spectroscopic studies

In this study, radish (Raphanus sativus L.) and common duckweed (Lemna minor L.) were treated with an aqueous dispersion of carboxylated silica-coated photon-upconversion nanoparticles containing rare-earth elements (Y, Yb, and Er). The total concentration of rare earths and their bioaccumulation factors were determined in root, hypocotyl, and leaves of R. sativus after 72 h, and in L. minor fronds after 168 h. In R. sativus, translocation factors were determined as the ratio of rare earths concentration in hypocotyl versus root and in leaves versus hypocotyl. The lengths of the root and hypocotyl in R. sativus, as well as the frond area in L. minor, were monitored as toxicity endpoints. To distinguish rare earth bioaccumulation patterns, two-dimensional maps of elemental distribution in the whole R. sativus plant and L. minor fronds were obtained by laser-induced breakdown spectroscopy with a lateral resolution of 100 μm. Moreover, the bioaccumulation was inspected using a photon-upconversion laser microscanner. The results revealed that the tested nanoparticles became adsorbed onto L. minor fronds and R. sativus roots, as well as transferred from roots through the hypocotyl and into leaves of R. sativus. The bioaccumulation patterns and spatial distribution of rare earths in nanoparticle-treated plants therefore differed from those of the positive control. Overall, carboxylated silica-coated photon-upconversion nanoparticles are stable, can easily translocate from roots to leaves, and are expected to become adsorbed onto the plant surface. They are also significantly toxic to the tested plants at nominal concentrations of 100 and 1000 μg/mL.

Click-conjugated photon-upconversion nanoparticles in an immunoassay for honeybee pathogen Melissococcus plutonius

European foulbrood (EFB) is an infectious disease affecting honeybee larvae caused by the bacterium Melissococcus plutonius. The enzyme-linked immunosorbent assay (ELISA) is the gold standard for antibody-based bacteria detection, however, its sensitivity is not high enough to reveal early-stage EFB infection. Photon-upconversion nanoparticles (UCNPs) are lanthanide-doped nanomaterials that emit light of shorter wavelength under near-infrared (NIR) excitation and thus avoid optical background interference. After conjugation with specific biorecognition molecules, UCNPs can be used as ultrasensitive labels in immunoassays. Here, we introduce a method for conjugation of UCNPs with streptavidin based on copper-free click chemistry, which involves surface modification of UCNPs with alkyne-modified bovine serum albumin (BSA) that prevents the non-specific binding and provides reactive groups for conjugation with streptavidin-azide. To develop a sandwich upconversion-linked immunosorbent assay (ULISA) for M. plutonius detection, we have prepared a rabbit polyclonal anti-Melissococcus antibody. The specific capture of the bacteria was followed by binding of biotinylated antibody and UCNP-BSA-streptavidin conjugate for a highly sensitive upconversion readout. The assay yielded an LOD of 340 CFU mL-1 with a wide working range up to 109 CFU mL-1, which is 400 times better than the LOD of the conventional ELISA. The practical applicability of the ULISA was successfully demonstrated by detecting M. plutonius in spiked real samples of bees, larvae and bottom hive debris. These results show a great potential of the assay for early diagnosis of EFB, which can prevent uncontrolled spreading of the infection and losses of honeybee colonies.