Poly(amino acid) Multilayers Modified Dendritic Mesoporous Silica Nanoparticles Achieve Effective Enzyme Stability for Ultrasensitive Immunoassay

Polypeptide-based multilayer nanoarchitectures: Controlled assembly on planar and colloidal substrates for biomedical applications

Polypeptides have shown an excellent potential in nanomedicine thanks to their biocompatibility, biodegradability, high functionality, and responsiveness to several stimuli. Polypeptides exhibit high propensity to organize at the supramolecular level; hence, they have been extensively considered as building blocks in the layer-by-layer (LbL) assembly. The LbL technique is a highly versatile methodology, which involves the sequential assembly of building blocks, mainly driven by electrostatic interactions, onto planar or colloidal templates to fabricate sophisticated multilayer nanoarchitectures. The simplicity and the mild conditions required in the LbL approach have led to the inclusion of biopolymers and bioactive molecules for the fabrication of a wide spectrum of biodegradable, biocompatible, and precisely engineered multilayer films for biomedical applications. This review focuses on those examples in which polypeptides have been used as building blocks of multilayer nanoarchitectures for tissue engineering and drug delivery applications, highlighting the characteristics of the polypeptides and the strategies adopted to increase the stability of the multilayer film. Cross-linking is presented as a powerful strategy to enhance the stability and stiffness of the multilayer network, which is a fundamental requirement for biomedical applications. For example, in tissue engineering, a stiff multilayer coating, the presence of adhesion promoters, and/or bioactive molecules boost the adhesion, growth, and differentiation of cells. On the contrary, antimicrobial coatings should repel and inhibit the growth of bacteria. In drug delivery applications, mainly focused on particles and capsules at the micro- and nano-meter scale, the stability of the multilayer film is crucial in terms of retention and controlled release of the payload. Recent advances have shown the key role of the polypeptides in the adsorption of genetic material with high loading efficiency, and in addressing different pathways of the particles/capsules during the intracellular uptake, paving the way for applications in personalized medicine. Although there are a few studies, the responsiveness of the polypeptides to the pH changes, together with the inclusion of stimuli-responsive entities into the multilayer network, represents a further key factor for the development of smart drug delivery systems to promote a sustained release of therapeutics. The degradability of polypeptides may be an obstacle in certain scenarios for the controlled intracellular release of a drug once an external stimulus is applied. Nowadays, the highly engineered design of biodegradable LbL particles/capsules is oriented on the development of theranostics that, limited to use of polypeptides, are still in their infancy.

Metal-organic framework-interfaced ELISA probe enables ultrasensitive detection of extracellular vesicle biomarkers

The enzyme-linked immunosorbent assay (ELISA) remains the prevailing method for quantifying protein biomarkers. Enzymatic signal generation and amplification are key mechanisms that govern its analytical performance. This study reports the synthesis and application of microscale metal-organic framework (MOF)/enzyme composite particles as a novel detection probe to substantially enhance the sensitivity of ELISA. An optimal one-pot approach was established to incorporate a substantial amount of streptavidin-horseradish peroxidase (SA-HRP) either within or on the surface of the metal-azolate framework (MAF-7) microparticles. This approach enables the labeling of a single sandwich antibody-antigen complex with numerous enzymes, which markedly amplifies the enzymatic colorimetric signal generation. Moreover, MAF-7 caging was found to enhance the reactivity of the caged HRP enzyme, further promoting the overall detection sensitivity of ELISA. Compared to other developments that are often associated with more complicated detection modalities, our method is compatible with standard immunoassays and commonly used photometrical signal detection. The implementation of this strategy in the detection of CD147 results in a remarkably low limit of detection of 2.8 fg mL-1, representing a 105-fold improvement compared to that obtained with the standard ELISA. Moreover, the heightened sensitivity of this technique renders it particularly suitable for diagnosing breast cancer, thus presenting a promising tool for the early detection of the disease in clinical settings.

A self-assembled 3D nanoflowers based nano-ELISA platform for the sensitive detection of pyridaben

Biomimetic methods are invariably employed to synthesize hybrid organic-inorganic multilevel structure nanoflowers with self-assembly processes in aqueous solutions, which is an ideal way to meet the challenges of immobilizing antibodies or enzymes in nanomaterial based enzyme-linked immunosorbent assay (nano-ELISA). In this study, we developed protein-inorganic hybrid 3D nanoflowers composed of bovine serum albumin (BSA), horseradish peroxidase (HRP)-conjugated goat anti-mouse IgG (IgG-HRP) and copper(Ⅱ) phosphate (BSA-(IgG-HRP)-Cu3(PO4)2) using a self-assembly biomimetic method. The preparation process avoided the use of any organic solvent and protein immobilization did not require covalent modifications. Additionally, the unique hierarchical structure enhances the thermal and storage stability of HRP. The BSA-(IgG-HRP)-Cu3(PO4)2 hybrid 3D nanoflower was then applied to a nano-ELISA platform for pyridaben detection, achieving a 50% inhibition concentration of 3.90 ng mL-1. The nano-ELISA achieved excellent accuracy for pyridaben detection. Such a novel BSA-(IgG-HRP)-Cu3(PO4)2 hybrid 3D nanoflower provide an excellent reagent for small molecule immunoassay.

Preparation of a capsaicinoids broad spectrum antibody and its application in non-enzyme immunoassay based on DMSNs@PDA@Pt

Capsaicinoids (CPCs) is a special ingredient with pungent smell in condiments, which can also be used as an exogenetic marker for kitchen waste oil. Development of immunoassay for CPCs remains a challenging due to relatively difficult preparation of the broad-spectrum antibody (Ab). In this work, a broad-spectrum polyclonal antibody (pAb) which can simultaneously recognize capsaicin (CPC), dihydrocapsaicin (DCPC), nordihydrocapsaicin (NDCPC), and N-vanillylnonanamide (N-V) is produced, and a non-enzyme immunoassay (NISA) based on this Ab, dendritic mesoporous silica nanomaterials (DMSNs), polydopamine (PDA), and high catalytic efficiency of Pt nanoparticles to prepare signal probe (DMSNs@PDA@Pt) is established. Here, the limit of detection (LOD) of NISA for CPC is as low as 0.04 μg L-1. It is worth mentioning that the LOD of the proposed NISA is at least 23 times lower than that of traditional enzyme-linked immunosorbent assay (ELISA) based on horseradish peroxidase (HRP). Moreover, the proposed NISA is applied to detect CPCs in edible oil samples, the result has good consistency with that of ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The proposed NISA based on DMSN@PDA@Pt and broad-spectrum Ab is an ideal tool for highly effective screening CPCs for kitchen waste oil abuse surveillance.

Enhancing Oriented Immobilization Efficiency: A One-for-Two Organism-Bispecific Nanobody Scaffold for Highly Sensitive Detection of Foodborne Pathogens

Nanobodies have gained widespread application in immunoassays. However, their small size presents a significant challenge in achieving effective immobilization and optimal sensitivity. Here, we present a novel "one-for-two"-oriented immobilization platform based on an organism-bispecific nanobody (O-BsNb) scaffold, enabling highly sensitive detection of two bacterial pathogens. Through genetic engineering, a bispecific nanobody (BsNb) was engineered, targeting Salmonella spp. and Vibrio parahaemolyticus. The O-BsNb scaffold allowed one nanobody to bind specifically to inactivated bacteria, forming an organism-oriented immobilization platform, while the other served as the capture antibody. Consequently, the O-BsNb bioscaffold-based ELISA (O-ELISA) for individual detection of S. enteritidis and V. parahaemolyticus was established. When compared to the sandwich ELISA utilizing passive immobilization of monovalent nanobodies, the O-ELISA exhibited a remarkable 13.4- and 13.7-fold improvement in LOD for S. enteritidis and V. parahaemolyticus, respectively, highlighting the enhanced immobilization efficacy of the O-ELISA. Furthermore, the feasibility and reproducibility of the assay in practical samples were meticulously evaluated, revealing exemplary performance in terms of recovery precision and assay stability. These findings demonstrate the significant potential of the O-ELISA platform for the sensitive detection of macromolecules, opening new avenues for efficient pathogen identification in foodborne safety and clinical diagnostics.

SARS-Cov-2 Spike-S1 Antigen Test Strip with High Sensitivity Endowed by High-Affinity Antibodies and Brightly Fluorescent QDs/Silica Nanospheres

The extensive research into developing novel strategies for detecting respiratory syndrome coronavirus 2 (SARS-CoV-2) antigens in clinical specimens, especially the sensitive point-of-care testing method, is still urgently needed to reach rapid screening of viral infections. Herein, a new lateral flow immunoassay (LFIA) platform was reported for the detection of SARS-CoV-2 spike-S1 protein antigens, in which four sensitive and specific SARS-CoV-2 mouse monoclonal antibodies (MmAbs) were tailored by using quantum dot (QD)-loaded dendritic mesoporous silica nanoparticles modified further for achieving the -COOH group surface coating (named Q/S-COOH nanospheres). Importantly, compact QD adsorption was achieved in mesoporous channels of silica nanoparticles on account of highly accessible central-radial pores and electrostatic interactions, leading to significant signal amplification. As such, a limit of detection for SARS-CoV-2 spike-S1 testing was found to be 0.03 ng/mL, which is lower compared with those of AuNPs-LFIA (traditional colloidal gold nanoparticles, Au NPs) and enzyme-linked immunosorbent assay methods. These results show that optimizing the affinity of antibody and the intensity of fluorescent nanospheres simultaneously is of great significance to improve the sensitivity of LFIA.

Synthesizing Submicron Polyelectrolyte Capsules to Boost Enzyme Immobilization and Enhance Enzyme-Based Immunoassays

Polyelectrolyte capsules (PCs) exhibit attractive superiorities in enzyme immobilization, including providing a capacious microenvironment for enzyme conformational freedom, highly effective mass transfer, and protecting enzymes from the external environment. Herein, we provide the first systemic evaluation of submicron PCs (SPCs, 500 nm) for enzyme immobilization. The catalytic kinetics results show that SPC encapsulation affected the affinities of enzymes and substrates but significantly enhanced their catalytic activity. The stability test indicates that SPC-encapsulated horseradish peroxidase (HRP) exhibits ultrahigh resistance to external harsh conditions and has a longer storage life than that of soluble HRP. The proposed encapsulation strategy enables 7.73-, 2.22-, and 11.66-fold relative activities when working at a pH as low as 3, at a NaCl concentration as high as 500 mM, and at a trypsin concentration as high as 10 mg/mL. We find that SPC encapsulation accelerates the cascade reaction efficiency of HRP and glucose oxidase. Owing to SPCs enhancing the catalytic activity of the loaded enzymes, we established an amplified enzyme-linked immunosorbent assay (ELISA) for the detection of Escherichia coli O157:H7 using HRP-loaded SPCs. The detection sensitivity of SPC-improved ELISA was found to be 280 times greater than that of conventional HRP-based ELISA. Altogether, we provide an elaborate evaluation of 500 nm SPCs on enzyme immobilization and its application in the ultrasensitive detection of foodborne pathogens. This evaluation provides evidence to reveal the potential advantage of SPCs on enzyme immobilization for enzyme-based immunoassays. It has excellent biological activity and strong stability and broadens the application prospect in urine, soy sauce, sewage, and other special samples.

Double-Enzyme Active Vanadium Nanospheres-Mediated Ratiometric Multicolor Immunosensors for Sensitive Detection of the T-2 Toxin

Owing to its high throughput, simplicity, and rapidity, enzyme-linked immunosorbent assay (ELISA) has attracted much attention in the field of immunoassays. However, the traditional ELISA usually affords a single signal readout and the labeling ability of the enzyme used is poor, resulting in low accuracy and a limited detection range. Herein, a vanadium nanospheres (VNSs)-mediated competitive ratio nanozymes-linked immunosorbent assay (VNSs-RNLISA) was created for the sensitive detection of the T-2 toxin (T-2). As the key to the biosensor, the VNSs with superoxide dismutase-like and peroxidase-like dual-enzyme mimetic activities were synthesized by a one-step hydrothermal method, which oxidized 1,1-diphenyl-2-picryl-hydrazyl fading and catalyzed 3,3',5,5'-tetramethylbenzidine (TMB) color development. Therefore, T-2 could not only be qualitatively measured with the naked eye but also be quantitatively evaluated by monitoring the ratio of absorbance at 450 and 517 nm wavelengths. Moreover, the characterization of a VNSs-labeled antibody probe showed strong dual-enzymatic activity, excellent stability, and high affinity with T-2 [the affinity constant (k_a) was approximately 1.36 × 10⁸ M^-1], which can significantly improve the detection sensitivity. The limit of detection of VNSs-RNLISA was 0.021 ng/mL, which was approximately 27-fold more sensitive than the single signal nanozymes-linked immunosorbent assay (0.561 ng/mL). Besides, the change in the ratio of absorbance (Δ450/Δ517) decreased linearly in a range of 0.22-13.17 ng/mL, outperforming the detection range of a single-mode nano-enzyme-linked immunosorbent assay using TMB by a factor of 1.6 times. Furthermore, the VNSs-RNLISA was successfully used to identify T-2 in maize and oat samples, with recoveries ranging from 84.216 to 125.371%. Overall, this tactic offered a promising platform for the quick detection of T-2 in food and might broaden the application range of the enzyme-linked immunosorbent assay.

Dual-Mode Immunosensor for Electrochemiluminescence Resonance Energy Transfer and Electrochemical Detection of Rabies Virus Glycoprotein Based on Ru(bpy)32+-Loaded Dendritic Mesoporous Silica Nanoparticles

Rabies is a serious zoonotic disease in almost all warm-blooded animals and causes fatal encephalitis. The detection of rabies virus (RABV) is critical and remains a significant challenge. Herein, an electrochemiluminescence resonance energy transfer (ECL-RET) and electrochemical (EC) dual-mode immunosensor was developed for highly sensitive detection of RABV glycoprotein. Dendritic mesoporous silica nanoparticles (DMSNs) were employed to load Ru(bpy)₃²⁺ and to obtain ECL probes (Ru@DMSNs). Ru@DMSNs were decorated on the electrode surface, followed by the modification of the RABV antibody (Ab₁). RABV was specifically recognized and captured by Ab₁, causing the decline of the ECL signal due to the obstruction of electron transfer. Additionally, manganese oxide nanoparticles (MnO_x) modified with Ab₂ can further quench the ECL signal of Ru@DMSNs via the RET between Ru@DMSNs and MnO_x. Meanwhile, MnO_x can catalyze the oxidation of o-phenylenediamine (o-PD), generating a significant differential pulse voltammetry (DPV) signal as a second signal to monitor RABV glycoprotein concentration. Consequently, an immunosensor was developed to achieve dual-signal detection of RABV and improve reliability. Under the optimal conditions, detection ranges of 0.10 pg·mL^-1 to 10 ng·mL^-1 for ECL (with an 88 fg·mL^-1 detection limit) and 1 pg·mL^-1 to 2 ng·mL^-1 for EC (with a 0.1 pg·mL^-1 detection limit) were obtained for RABV detection. The reliability of this immunoassay was validated by eight brain tissue samples. The results were found to be compatible with the results of the real-time reverse transcription-polymerase chain reaction (RT-PCR) assay, indicating the potential applicability of this method for RABV diagnosis.

Modified ELISA for Ultrasensitive Diagnosis

An enzyme-linked immunosorbent assay (ELISA) can be used for quantitative measurement of proteins, and improving the detection sensitivity to the ultrasensitive level would facilitate the diagnosis of various diseases. In the present review article, we first define the term 'ultrasensitive'. We follow this with a survey and discussion of the current literature regarding modified ELISA methods with ultrasensitive detection and their application for diagnosis. Finally, we introduce our own newly devised system for ultrasensitive ELISA combined with thionicotinamide adenine dinucleotide cycling and its application for the diagnosis of infectious diseases and lifestyle-related diseases. The aim of the present article is to expand the application of ultrasensitive ELISAs in the medical and biological fields.

Magnetic nanochains-based dynamic ELISA for rapid and ultrasensitive detection of acute myocardial infarction biomarkers

Acute myocardial infarction (AMI) is the leading cause of morbidity and mortality globally. The serum levels of a group of cardiac biomarkers have been regarded as important indicators in the routine diagnosis of AMI. The development of rapid, sensitive, and accurate detection methods of AMI biomarkers is urgently needed for the early diagnosis of AMI. Here, a dynamic and pseudo-homogeneous enzyme-linked immunosorbent assay (ELISA) was reported based on the combined use of bioconjugated magnetic nanochains (MNCs) and gold nanoparticles (AuNPs) probes. The capture antibodies-conjugated MNCs served as dynamic nano-mixers to facilitate liquid mixing and as homogeneously dispersed capturing agents to capture and separate specific targets. The AuNPs probes were prepared by co-immobilization of detection antibodies and horseradish peroxidase (HRP) for signals amplification. The design of bioconjugated MNCs and AuNPs probes significantly increased the assay kinetics and improves the assay sensitivity. This novel ELISA strategy realized accurate detection of a panel of AMI biomarkers within 35 min, leading to considerably improved sensitivities compared to that of conventional ELISA method.

Aptamers as the powerhouse of dot blot assays

Dot blot assays have always been associated with antibodies as the main molecular recognition element, which are widely employed in a myriad of diagnostic applications. With the rising of aptamers as the equivalent molecular recognition elements of antibodies, dot blot assays are also one of the diagnostic avenues that should be scrutinized for their amenability with aptamers as the potential surrogates of antibodies. In this review, the stepwise procedures of an aptamer-based dot blot assays are underscored before reviewing the existing aptamer-based dot blot assays developed so far. Most of the applications center on monitoring the progress of SELEX and as the validatory assays to assess the potency of aptamer candidates. For the purpose of diagnostics, the current effort is still languid and as such possible suggestions to galvanize the move to spur the aptamer-based dot blot assays to a point-of-care arena are discussed.