Progress in Procalcitonin Detection Based on Immunoassay

Procalcitonin (PCT) serves as a crucial biomarker utilized in diverse clinical contexts, including sepsis diagnosis and emergency departments. Its applications extend to identifying pathogens, assessing infection severity, guiding drug administration, and implementing theranostic strategies. However, current clinical deployed methods cannot meet the needs for accurate or real-time quantitative monitoring of PCT. This review aims to introduce these emerging PCT immunoassay technologies, focusing on analyzing their advantages in improving detection performances, such as easy operation and high precision. The fundamental principles and characteristics of state-of-the-art methods are first introduced, including chemiluminescence, immunofluorescence, latex-enhanced turbidity, enzyme-linked immunosorbent, colloidal gold immunochromatography, and radioimmunoassay. Then, improved methods using new materials and new technologies are briefly described, for instance, the combination with responsive nanomaterials, Raman spectroscopy, and digital microfluidics. Finally, the detection performance parameters of these methods and the clinical importance of PCT detection are also discussed.

Ultrasensitive and Rapid Detection of Procalcitonin via Waveguide-Enhanced Nanogold-Linked Immunosorbent Assay for Early Sepsis Diagnosis

Sepsis, a life-threatening inflammatory response, demands economical, accurate, and rapid detection of biomarkers during the critical "golden hour" to reduce the patient mortality rate. Here, we demonstrate a cost-effective waveguide-enhanced nanogold-linked immunosorbent assay (WENLISA) based on nanoplasmonic waveguide biosensors for the rapid and sensitive detection of procalcitonin (PCT), a sepsis-related inflammatory biomarker. To enhance the limit of detection (LOD), we employed sandwich assays using immobilized capture antibodies and detection antibodies conjugated to gold nanoparticles to bind the target analyte, leading to a significant evanescent wave redistribution and strong nanoplasmonic absorption near the waveguide surface. Experimentally, we detected PCT for a wide linear response range of 0.1 pg/mL to 1 ng/mL with a record-low LOD of 48.7 fg/mL (3.74 fM) in 8 min. Furthermore, WENLISA has successfully identified PCT levels in the blood plasma of patients with sepsis and healthy individuals, offering a promising technology for early sepsis diagnosis.

An ultrasensitive NIR-IIa' fluorescence-based multiplex immunochromatographic strip test platform for antibiotic residues detection in milk samples

INTRODUCTION

Widely used in livestock breeding, residues of antibiotic drugs in milk have become a threat to food safety and human health. Current rapid detection technologies using colorimetric immunochromatographic strip tests (IST) lack the necessary sensitivity for on-site trace monitoring. Fluorescence-based detection in the near-infrared IIa' (NIR-IIa') region (1000 ∼ 1300 nm) has enormous potential due to greatly minimized auto-fluorescence and light scattering.

OBJECTIVES

The aim of this work is to develop an ultrasensitive IST platform using NIR-IIa' fluorescent nanoparticles as labels for multiplex antibiotic residues detection in milk.

METHODS

NIR-IIa' fluorescent nanoparticles were assembled by encapsulating synthesized NIR-IIa' fluorophores into carboxyl - modified polystyrene nanoparticles. The NIR-IIa' nanoparticles were subsequently used as labels in an IST platform to detect sulfonamides, quinolones, and lincomycin simultaneously in milk. A portable fluorescent reader was fabricated to provide on-site detection. To further validate the developed IST platform, the detection was compared with LC-MS/MS in 22 real milk samples.

RESULTS

Fluorescent nanoparticles were synthesized with low energy emission (1030 nm) and large Stokes shift (>250 nm) showing a much higher signal-to-noise ratio compared with fluorophores emitting in the NIR-I region. The developed IST platform yielded a highly sensitive, simultaneous quantification of sulfonamides, quinolones, and lincomycin in milk with detection limits of 46.7, 27.6 and 51.4 pg/mL, respectively, achieving a wide detection range (up to 50 ng/mL). The IST platform showed good accuracy, reproducibility, and specificity with the portable fluorescent reader which could rapidly quantify in 10 s. These results were better than reported immunochromatographic assays using fluorescent labels, and remarkably, showed a higher recognition ability than LC-MS/MS for real samples.

CONCLUSION

The utility of NIR-IIa' fluorescence-based IST platform for the fast, sensitive, and accurate detection of antibiotics in milk was demonstrated, successfully verifying the potential of this platform in detecting trace materials in complex matrices.

Advantages of aggregation-induced luminescence microspheres compared with fluorescent microspheres in immunochromatography assay with sandwich format

Organic fluorescein dye-embedded fluorescent microspheres (FMs) are currently the most established commercially fluorescent markers, and they have been widely used to improve the sensitivity of immunochromatography assay (ICA). However, these FMs have natural defects, such as the aggregation-caused quenching effect and small Stokes shift, which are not conducive to improving the detection performance of ICA. Herein, two green emitted FMs, namely aggregation-induced emission FMs (AIEFMs) and fluorescein isothiocyanate FMs (FITCFMs), were prepared by swelling the AIE luminogens and FITC dyes into the carboxyl group-modified polystyrene microspheres. The average diameters of AIEFMs and FITCFMs were 350 and 450 nm, respectively. Compared with FITCFMs, the AIEFMs exhibited stronger fluorescence intensity and a larger Stokes shift. These two FMs were used as the labeling markers of ICA for procalcitonin (PCT) detection with the sandwich format. Among them, AIEFM-ICA showed dynamic linear detection of PCT from 7.6 pg mL^-1 to 125 ng mL^-1 with the limit of detection (LOD) at 3.8 pg mL^-1. These values were remarkably superior to those of FITCFM-ICA (linear range from 61 pg mL^-1 to 62.5 ng mL^-1 and LOD value at 60 pg mL^-1). Furthermore, the average recoveries of the intra- and inter-assays of AIEFM-ICA ranged from 86% to 112%, with coefficients of variation ranging from 1.2% to 8.8%, indicating accuracy and precision for PCT quantitative detection. Additionally, the reliability of the developed AIEFM-ICA was further assessed by analyzing 30 real serum samples from systemic inflammatory response by infectious diseases, and the results showed good agreement with the chemiluminescence immunoassay. In conclusion, compared with traditional FITCFMs, green emitted AIEFMs as a novel fluorescent label, exhibits greater potential to enhance the detection performance of the ICA platform.

Eu-Chelate Polystyrene Microsphere-Based Lateral Flow Immunoassay Platform for hs-CRP Detection

Inflammation caused by viral or bacterial infection is a major threat to human health globally. Blood C-reactive protein (CRP) has been proven to be a sensitive indicator for the occurrence and development of inflammation. Furthermore, a tiny change of blood CRP concentration may portend chronic diseases; therefore, high-sensitivity CRP (hs-CRP) detection in a quantitative, rapid, user-friendly, and low-cost manner is highly demanded. In this paper, we developed a europium-chelate polystyrene microsphere (EuPSM)-based lateral flow immunoassay (LFIA) integrating with a benchtop fluorescence analyzer for hs-CRP detection. The optimization of the EuPSM-based LFIA was implemented through adjusting the antibody density on EuPSM from 100% to 60% of the saturated density. Finally, the limit of detection of 0.76 pg/mL and detection range of 0.025-250 ng/mL were obtained. Moreover, the clinical application capability of the proposed platform was validated through detecting CRP in clinical serum samples, showing high consistency with the results obtained from the clinical standard method. Hence, the proposed EuPSM-based LFIA has been verified to be well suitable for hs-CRP detection, while also showing great applicability for sensitively and rapidly detecting other biomarkers.

Dye-sensitized lanthanide containing nanoparticles for luminescence based applications

Due to their exceptional luminescent properties, lanthanide (Ln) complexes represent a unique palette of probes in the spectroscopic toolkit. Their extremely weak brightness due to forbidden Ln electronic transitions can be overcome by indirect dye-sensitization from the antenna effect brought by organic ligands. Despite the improvement brought by the antenna effect, (bio)analytical applications with discrete Ln complexes as luminescent markers still suffers from low sensitivity as they are limited by the complex brightness. Thus, there is a need to develop nano-objects that cumulate the spectroscopic properties of multiple Ln ions. This review firstly gives a brief introduction of the spectral properties of lanthanides both in complexes and in nanoparticles (NPs). Then, the research progress of the design of Ln-doped inorganic NPs with capping antennas, Ln-complex encapsulated NPs and Ln-complex surface functionalized NPs is presented along with a summary of the various photosensitizing ligands and of the spectroscopic properties (excited-state lifetime, brightness, quantum yield). The review also emphasizes the problems and limitations encountered over the years and the solutions provided to address them. Finally, a comparison of the advantages and drawbacks of the three types of NP is provided as well as a conclusion about the remaining challenges both in the design of brighter NPs and in the luminescence based applications.

Development of a time-resolved fluorescence microsphere Eu lateral flow test strip based on a molecularly imprinted electrospun nanofiber membrane for determination of fenvalerate in vegetables

Fenvalerate residues in fruits and vegetables may result in biological immune system disorders. Current sensor detection methods are harsh due to the shortcomings of antibody preparation and preservation conditions. Therefore, developing a recognition material with strong specificity, good stability, and low cost is of practical significance in designing a sensitive, simple, and rapid method. This study used precipitation polymerization to synthesize molecularly imprinted polymers (MIPs). The MIP was prepared into a fiber membrane using the electrostatic spinning method. After that, the fenvalerate hapten-mouse IgG-Eu fluorescent probe was synthesized, and the side flow chromatography strip was constructed to determine fenvalerate in vegetables using the immunocompetition method. The results showed that the adsorption capacity of MIP to fenvalerate was 3.65, and the adsorption capacity on MIPFM (an electrospinning membrane containing the fenvalerate MIPs) was five times that of free MIP. The test strip showed good linearity with R 2 = 0.9761 within the range of 50 μg/L-1,000 μg/L. In conclusion, substituting fenvalerate monoclonal antibodies with a molecularly imprinted electrospinning membrane is ideal for rapid onsite detection of pyrethroids.

Recent Advances in the Recognition Elements of Sensors to Detect Pyrethroids in Food: A Review

The presence of pyrethroids in food and the environment due to their excessive use and extensive application in the agriculture industry represents a significant threat to public health. Therefore, the determination of the presence of pyrethroids in foods by simple, rapid, and sensitive methods is warranted. Herein, recognition methods for pyrethroids based on electrochemical and optical biosensors from the last five years are reviewed, including surface-enhanced Raman scattering (SERS), surface plasmon resonance (SPR), chemiluminescence, biochemical, fluorescence, and colorimetric methods. In addition, recognition elements used for pyrethroid detection, including enzymes, antigens/antibodies, aptamers, and molecular-imprinted polymers, are classified and discussed based on the bioreceptor types. The current research status, the advantages and disadvantages of existing methods, and future development trends are discussed. The research progress of rapid pyrethroid detection in our laboratory is also presented.

Novel Organic-Inorganic Hybrid Polystyrene Nanoparticles with Trichromatic Luminescence for the Detection of Latent Fingerprints

This article explored the application of novel organic-inorganic hybrid polystyrene nanoparticles (PSNPs) with trichromatic luminescence for the detection of latent fingerprints. The PSNPs were synthesized by encapsulated Eu(DBM)3phen, coumarin 6, and FDBT into the polystyrene nanoparticles through the swelling method and applied them to visualize latent fingerprints. The PSNPs had a spherical morphology with an average diameter of 310.7 nm, and they emitted trichromatic fluorescence (525 nm/570 nm/610 nm) under 365 nm excitation wavelength with green/yellow/red color under filters. They were less likely to aggregate, float or stain the background when treating fingerprints. The developed fingerprints with excellent clarity of ridges and contrast could be viewed, and the digital magnification of fluorescence-developed fingerprints provided more minutiae details about some regional patterns. The colorimetric and fluorescent trichromatic light could provide complementary signals without the background interference from fluorescent substrates and/or complex multicolor surfaces, which improved the applicability of fluorescent nanoparticles for fingerprints development. PSNPs are promising for the detection of latent fingerprints and practical criminal investigations with their ease of operation, eco-friendly properties, and excellent trichromatic optical performance.

Paper-based analytical devices for virus detection: Recent strategies for current and future pandemics

The importance of user-friendly, inexpensive, sensitive, and selective detection of viruses has been highlighted again due to the recent Coronavirus disease 2019 (COVID-19) pandemic. Among the analytical tools, paper-based devices (PADs) have become a leading alternative for point-of-care (POC) testing. In this review, we discuss the recent development strategies and applications in nucleic acid-based, antibody/antigen-based and other affinity-based PADs using optical and electrochemical detection methods for sensing viruses. In addition, advantages and drawbacks of presented PADs are identified. Current state and insights towards future perspectives are presented regarding developing POC diagnosis platform for COVID-19. This review considers state-of-the-art technologies for further development and improvement in PADs performance for virus detection.

Luminescent lanthanide nanoparticle-based imaging enables ultra-sensitive, quantitative and multiplexed in vitro lateral flow immunoassays

Lateral Flow Assays (LFAs) have been extensively used on-site to rapidly detect analytes, possibly in complex media. However, standard gold nanoparticle-based LFAs lack sensitivity and cannot provide quantitative measurements with high accuracy. To overcome these limitations, we image lanthanide-doped nanoparticles (YVO₄:Eu 40%) as new luminescent LFA probes, using a homemade reader coupled to a smartphone and propose an original image analysis allowing strip quantification regardless of the shape of the test band signal. This method is demonstrated for the detection of staphylococcal enterotoxins SEA, SEG, SEH, and SEI. A systematic comparison to state-of-the-art gold nanoparticle-based LFA revealed an analytical sensitivity enhancement of at least one order of magnitude. We furthermore provided measurements of absolute toxin concentration over two orders of magnitude and demonstrated simultaneous quantitative detection of multiple toxins with unaltered sensitivity. In particular, we reached concentrations 100 times lower than the ones reported in the literature for on-site multiplexed LFA targeting enterotoxins. Altogether, these results highlight that our luminescent nanoparticle-based method provides a powerful and versatile on-site framework to detect multiple biomolecules with sensitivity approaching that obtained by ELISA. This paves the way to a change of paradigm in the field of analytical immunoassays by providing fast in situ quantitative high sensitivity detection of biomarkers or pathogens.

State-of-the-Art of Nanodiagnostics and Nanotherapeutics against SARS-CoV-2

The pandemic outbreak of SARS-CoV-2, with millions of infected patients worldwide, has severely challenged all aspects of public health. In this regard, early and rapid detection of infected cases and providing effective therapeutics against the virus are in urgent demand. Along with conventional clinical protocols, nanomaterial-based diagnostics and therapeutics hold a great potential against coronavirus disease 2019 (COVID-19). Indeed, nanoparticles with their outstanding characteristics would render additional advantages to the current approaches for rapid and accurate diagnosis and also developing prophylactic vaccines or antiviral therapeutics. In this review, besides presenting an overview of the coronaviruses and SARS-CoV-2, we discuss the introduced nanomaterial-based detection assays and devices and also antiviral formulations and vaccines for coronaviruses.

Rapid and Sensitive Detection of anti-SARS-CoV-2 IgG, Using Lanthanide-Doped Nanoparticles-Based Lateral Flow Immunoassay

The outbreak of 2019 coronavirus disease (COVID-19) has been a challenge for hospital laboratories because of the huge number of samples that must be tested for the presence of the causative pathogen, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Simple and rapid immunodiagnostic methods are urgently needed to identify positive cases. Here we report the development of a rapid and sensitive lateral flow immunoassay (LFIA) that uses lanthanide-doped polysterene nanoparticles (LNPs) to detect anti-SARV-CoV-2 IgG in human serum. A recombinant nucleocapsid phosphoprotein of SARS-CoV-2 was dispensed onto a nitrocellulose membrane to capture specific IgG. Mouse anti-human IgG antibody was labeled with self-assembled LNPs that served as a fluorescent reporter. A 100-μL aliquot of serum samples (1:1000 dilution) was used for this assay and the whole detection process took 10 min. The results of the validation experiment met the requirements for clinical diagnostic reagents. A value of 0.0666 was defined as the cutoff value by assaying 51 normal samples. We tested 7 samples that were positive by reverse-transcription (RT-)PCR and 12 that were negative but clinically suspicious for the presence of anti-SARS-CoV-2 IgG. One of the negative samples was determined to be SARS-CoV-2 IgG positive, while the results for the other samples were consistent with those obtained by RT-PCR. Thus, this assay can achieve rapid and sensitive detection of anti-SARS-CoV-2 IgG in human serum and allow positive identification in suspicious cases; it can also be useful for monitoring the progression COVID-19 and evaluating patients' response to treatment.

Rapid and Sensitive Detection of anti-SARS-CoV-2 IgG, Using Lanthanide-Doped Nanoparticles-Based Lateral Flow Immunoassay

The outbreak of 2019 coronavirus disease (COVID-19) has been a challenge for hospital laboratories because of the huge number of samples that must be tested for the presence of the causative pathogen, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Simple and rapid immunodiagnostic methods are urgently needed to identify positive cases. Here we report the development of a rapid and sensitive lateral flow immunoassay (LFIA) that uses lanthanide-doped polysterene nanoparticles (LNPs) to detect anti-SARV-CoV-2 IgG in human serum. A recombinant nucleocapsid phosphoprotein of SARS-CoV-2 was dispensed onto a nitrocellulose membrane to capture specific IgG. Mouse anti-human IgG antibody was labeled with self-assembled LNPs that served as a fluorescent reporter. A 100-μL aliquot of serum samples (1:1000 dilution) was used for this assay and the whole detection process took 10 min. The results of the validation experiment met the requirements for clinical diagnostic reagents. A value of 0.0666 was defined as the cutoff value by assaying 51 normal samples. We tested 7 samples that were positive by reverse-transcription (RT-)PCR and 12 that were negative but clinically suspicious for the presence of anti-SARS-CoV-2 IgG. One of the negative samples was determined to be SARS-CoV-2 IgG positive, while the results for the other samples were consistent with those obtained by RT-PCR. Thus, this assay can achieve rapid and sensitive detection of anti-SARS-CoV-2 IgG in human serum and allow positive identification in suspicious cases; it can also be useful for monitoring the progression COVID-19 and evaluating patients' response to treatment.

Homogeneous and high-density gold unit implanted optical labels for robust and sensitive point-of-care drug detection

Controllable integration of gold building blocks into mesoscopic architecture produces improved optical signals with preferable stability for biological sensing. Here, we developed novel optical labels with homogeneous and high-density implanted hydrophobic gold nanoparticles (AuNPs) throughout three-dimensional silica scaffolds. The dendritic silica supports with an extra-large pore size and highly accessible central-radial channels were employed as metal-affinity templates, for anchoring with AuNPs directly from the organic phase. The nano-assemblies exhibited a high unit loading capacity while maintaining the intrinsic optical characteristics of AuNPs. After phase transfer by the alkylsilane intermediate layer and exterior silica shell encapsulation, the nanocomposites revealed an amplified plasmonic absorption signal, excellent colloidal/optical stability and convenient surface functionalization. By integrating the silica labels into the lateral flow immunoassay strip for signal enhancement, the sensitive point-of-care detection of methamphetamine in urine was established. The limit of detection achieved 0.026 ng mL-1, with a detection range from 0.023 to 375 ng mL-1 in a 10 min assay, allows both visual and on-site quantitative analysis. Encouragingly, the potential interfering drugs in the sample matrix showed a negligible influence on the results, validating the superior specificity of the current immunoassay. The newly developed gold-implanted optical labels show prospects for point-of-care testing in a complex biological matrix with the desirable stability and signal amplification.

A semi-quantitative rapid multi-range gradient lateral flow immunoassay for procalcitonin

A rapid semi-quantitative gradient lateral flow immunoassay (LFIA) of procalcitonin (PCT), a peptide precursor of the hormone calcitonin, was developed. The method is based on particular analyte cut-offs by immobilizing specific antibodies on the test strip with a consistent (gradient) increase in concentration from line to line. Semi-quantitative multi-range analysis is evaluated visually by counting the number of colored test lines corresponding to a certain concentration range of sepsis marker: [PCT]˂0.25; 0.25 ≤ [PCT] < 0.5; 0.5 ≤ [PCT] < 2; 2 ≤ [PCT] < 10; [PCT] ≥ 10 ng·mL^-1. This multi-range gradient LFIA was implemented by using two types of label: spherical gold nanoparticles (35 nm) and hierarchical popcorn-like gold nanoparticles (100 nm). The comparison of this LFIA with an ELISA (for n = 82) yielded 87.5% and 76.6% sensitivities, and 92.3% and 92.3% specificities, respectively. Thus, multi-range gradient LFIA performs well at PCT thresholds, which is important for early diagnosis of sepsis and severe bacterial infection. In our perception, this method has a wide scope in that it may be implemented in numerous other LFIA based test systems. Graphical abstract Schematic of the gradient lateral flow immunoassay for determination of clinically relevant procalcitonin ranges. It allows to reach the correlation between the number of developed test lines and procalcitonin concentration range in serum by pre-immobilization of capture antibodies in a consistently (gradient) increasing concentration.

Fluorometric determination of ciprofloxacin using molecularly imprinted polymer and polystyrene microparticles doped with europium(III)(DBM)3phen

The authors describe a microparticle-based system for the detection of the fluoroquinolone antibiotic ciprofloxacin. The method is using the tris(dibenzoylmethane)(1,10-phenanthroline)europium(III) luminophore in polystyrene microparticles along with a molecularly imprinted polymer (MIP) for ciprofloxacin. If ciprofloxacin is captured by the MIP, it quenches the fluorescence of the luminophores. Fluorescence drops linearly in the 0.5-100 μg L^-1 ciprofloxacin concentration range, and the detection limit is 92 ng L^-1. The method was applied to the analysis of fish samples to assess the analytical performance of the probe. Recoveries ranged from 85.4 to 86.6%, and relative standard deviations between 2.1 and 3.9% (for n = 5). Graphical abstract Schematic presentation of a microparticle-based probe using the tris(dibenzoylmethane)(1,10-phenanthroline)europium(III) luminophore in polystyrene particles along with a molecularly imprinted polymer for ciprofloxacin. After removal of template, carboxylic groups left in the probe can bind to ciprofloxacin through hydrogen bonds.

Bio-inspired microcapsule for targeted antithrombotic drug delivery

Thrombosis or embolism is the leading cause of death and long-term adult disability worldwide. To reduce the risk of thrombosis and hemorrhaging in patients, a facile and versatile method was developed to fabricate microcapsules for targeted antithrombotic drug delivery. The microcapsules were prepared via oxidative polymerization of dopamine on polystyrene microspheres, followed by immobilization of fibrinogen onto the surface of poly(dopamine) layers. Subsequently, microcapsules were obtained by removing the cores with THF. Nattokinase was loaded into the microcapsules via diffusion. The loading amount was approximately 0.05 mg g⁻¹ at 37 °C, and the loading efficiency was nearly 75%, based on the initial concentration of nattokinase in PBS. The release of nattokinase was a gradual process at 37 °C, and the activity of the targeted activated platelets was highly efficient. The antithrombotic activity of the nattokinase microcapsules was evidenced by the sharp dissolution of fibrin clots and the blood clotting time indexes. A gradual release mechanism of platelet-inspired microcapsules used for targeted antithrombotic therapy was proposed. This strategy for targeted antithrombotic drug delivery, which lowers the demand dose and minimizes side effects while maximizing drug efficacy, provides a potential new way to treat life-threatening diseases caused by vascular disruption.

NK-loaded hollow microcapsules were fabricated and assessed as a potential antithrombosis therapy.

Lanthanide-Doped Nanoparticles for Diagnostic Sensing

Lanthanide-doped nanoparticles exhibit unique optical properties, such as a long luminescence lifetime (up to several milliseconds), sharp emission peaks, and upconversion luminescence over the range of wavelengths from near-infrared to visible. Exploiting these optical properties, lanthanide-doped nanoparticles have been widely utilized for cellular and small animal imaging with the absence of background autofluorescence. In addition, these nanoparticles have advantages of high signal-to-noise ratio for highly sensitive and selective diagnostic detection. In this review, we summarize and discuss recent progress in the development of highly sensitive diagnostic methods using lanthanide-doped nanoparticles. Combined with a smartphone, portable luminescence detecting platforms could be widely applied in point-of-care tests.