A sandwich-type electrochemical immunosensor based on spherical nucleic acids-templated Ag nanoclusters for ultrasensitive detection of tumor biomarker

An ingenious electrochemical system based on naphthalenediimide derivatives for ultrasensitive immunosensing of alpha-fetoprotein

It is crucial to develop highly efficient electrochemistry systems for sensitive detection of tumour markers. In this work, naphthalenediimide derivatives with electrochemical application potential were successfully synthesized and characterized. Electrochemistry and calculation of density functional theory (DFT) showed that 2,7-bis(4-(dimethylamino)phenyl)benzo[lmn] [3,8]phenanthroline-1,3,6,8(2H,7H)-tetraone (NDI-1) was an ideal candidate for electrochemical probe construction. Subsequently, based on the cyclic catalytic effect between NDI-1 and K2S2O8, a satisfying composite of GO/NDI-1/AuNPs was prepared and used to construct electrochemical probe for the design of ingenious sandwiched electrochemical immunosensor. Taking alpha-fetoprotein (AFP) as the model target biomarker, the designed immunosensor showed good detection performance for AFP, which exhibited wide range of linear response (10 fg/mL - 10 ng/mL), low detection limit (3.3 fg/mL). Moreover, the proposed immunosensor has been successfully applied to AFP detection in human serum, which provides the possibility for clinical applications. The designed electrochemical system provides a new electrochemical probe for the construction of immunosensors and may be extended to the electroanalysis of other biomolecules with recognition units.

Advanced laser-induced graphene-based electrochemical immunosensor for the detection of C-reactive protein

C-reactive protein (CRP) is a critical biomarker for detecting inflammation and forecasting cardiovascular disease. We present an advanced electrochemical immunosensor utilizing laser-induced graphene (LIG)/MXene-gold nanoparticles (Mx-AuNPs) electrode for CRP detection. The Mx-AuNPs nanocomposite, synthesized via in-situ reduction of HAuCl4 by MXene, leverages MXene's reducing properties for effective nanoparticle deposition, confirmed through scanning electron microscopy. This electrode demonstrates superior electrochemical performance due to enhanced surface area and synergy between LIG and Mx-AuNPs, improving overall electrode conductivity. The Anti-CRP antibody, immobilized via a cysteamine linker, enables CRP detection. The immunosensor achieves excellent detection across 10 pg mL-1 to 10 µg mL-1 CRP, with a low detection limit of 1.45 pg mL-1, and shows high selectivity for CRP. This LIG/Mx-AuNPs-based immunosensor is promising for sensitive CRP detection, aiding early cardiovascular disease diagnosis and improving patient outcomes.

Lectin-Mediated Labeling of Alkaline Phosphatase for Enzymatic Silver Deposition-Based Electrochemical Detection of Glycoprotein Tumor Markers

The screening of glycoprotein markers has become an integral part of the in vitro diagnosis of malignant tumors. Herein, an electrochemical method based on alkaline phosphatase (ALP)-mediated enzymatic silver deposition is reported for the highly sensitive detection of glycoprotein tumor markers, in which ALP enzymes are decorated to the glycan moieties of targets via the lectin-carbohydrate interactions. As glycoproteins are conjugated with multiple glycan chains, lectin-mediated labeling can result in the decoration of each target with multiple ALP enzymes. Moreover, the enzymatic hydrolysis of ascorbic acid 2-phosphate into ascorbic acid can result in the deposition of a high density of silver particles, which can then be sensitively assayed via the robust Ag/AgCl solid-state voltammetric process. As a result, the enzymatic silver deposition-based electrochemical method exhibits high sensitivity. Using the aptamer-based electrochemical detection of the breast cancer-associated glycoprotein CA15-3 as a proof of concept, a detection limit of 0.32 mU/mL has been demonstrated. Results show that the synergism of the aptamer-based capture and the glycoform-specific discrimination capability of the lectin-carbohydrate interactions can endow this method with high selectivity, and its practical use in the assay of CA15-3 levels in serum samples has been illustrated. With benefits from the high efficiency, mild reaction conditions, and user-friendly operation, the lectin-mediated labeling of ALP enzymes for enzymatic silver deposition is highly applicable to the electrochemical detection of low-abundance glycoprotein tumor markers.

In Vivo Interactions of Nucleic Acid Nanostructures With Cells

Nucleic acid nanostructures, derived from the assembly of nucleic acid building blocks (e.g., plasmids and oligonucleotides), are important intracellular carriers of therapeutic cargoes widely utilized in preclinical nanomedicine applications, yet their clinical translation remains scarce. In the era of "translational nucleic acid nanotechnology", a deeper mechanistic understanding of the interactions of nucleic acid nanostructures with cells in vivo will guide the development of more efficacious nanomedicines. This review showcases the recent progress in dissecting the in vivo interactions of four key types of nucleic acid nanostructures (i.e., tile-based, origami, spherical nucleic acid, and nucleic acid nanogel) with cells in rodents over the past five years. Emphasis lies on the cellular-level distribution of nucleic acid nanostructures in various organs and tissues and the cellular responses induced by their cellular entry. Next, in the spirit of preclinical translation, this review features the latest interactions of nucleic acid nanostructures with cells in large animals and humans. Finally, the review offers directions for studying the interactions of nucleic acid nanostructures with cells from both materials and biology perspectives and concludes with some regulatory updates.

Sensitive electrochemical immunosensor for rapid detection of Salmonella in milk using polydopamine/CoFe-MOFs@Nafion modified gold electrode

Food contaminated by pathogenic bacteria poses a serious threat to human health. Consequently, we used Salmonella as a model and developed an electrochemical immunosensor based on a polydopamine/CoFe-MOFs@Nafion nanocomposite for the detection of Salmonella in milk. The CoFe-MOFs exhibit good stability, large specific surface area, and high porosity. However, after modification on the electrode surface, they were prone to detachment. This issue was effectively mitigated by incorporating Nafion into the nanocomposite. A polydopamine (PDA) film was deposited onto the surface of CoFe-MOFs@Nafion through cyclic voltammetry (CV), accompanied by an investigation into the polymerization mechanism of the PDA film. PDA contains a substantial number of quinone functional groups, which can covalently bind to amino or sulfhydryl groups via Michael addition reaction or Schiff base reaction, thereby immobilizing anti-Salmonella antibodies onto the modified electrode surface. Under the optimal experimental conditions, the Salmonella concentration exhibited a good linear relationship within the range of 1.38 × 102 to 1.38 × 108 CFU mL-1, with a detection limit of 1.38 × 102 CFU mL-1. Furthermore, the constructed immunosensor demonstrated good specificity, stability, and reproducibility, offering a novel approach for the rapid detection of foodborne pathogens.

Au NPs modified Ni-B nanosheets/graphene oxide three-dimensional network as label-free electrochemical immunosensor for the detection of diethylstilbestrol

Three-dimensional (3D) network provide a promising platform for construction of high sensitive electrochemical immunosensor due to the benefits of high specific surface area and electron mobility. Herein, a sensitive label-free electrochemical immunosensor based on Au nanoparticles modified Ni-B nanosheets/graphene matrix was constructed to detect diethylstilbestrol (DES). The 3D network not only could increase the electron transport rate and surface area, but also could provide confinement area, which is conducive to increases the collision frequency with the active site. Moreover, Au NPs also have good biocompatibility, which is beneficial for ligating antibodies. Benefiting from the 3D network structure and Au collective effect, the electrochemical immunosensor possess sterling detection ability with wide linear response range (0.00038-150 ng/mL) and low detection limit (31.62 fg/mL). Moreover, the constructed immunosensor can also be extend to detect DES in Tap-water and river water. This work may provide a novel material model for the construction of high sensitive immunosensor.

The fabrication of phosphotungstate@UIO-Au/reduced graphene oxidation for electrochemical ultrasensitive detection of alpha-fetoprotein

As an early multi-purpose tumor marker of hepatocellular carcinoma, alpha-fetoprotein (AFP) plays a vital role in early diagnosis and treatment. To achieve the early and accurate determination of AFP, the POMOF was fabricated by embedding H3PW12O40 (PW12) into UIO-66-NH2, further immobilized on reduced GO (rGO) and fabricated an innovative POMOF nanocomposite (PW@UIO-Au/rGO) as an electrochemical immunosensor (ECI-sensor). The PW@UIO-Au/rGO achieved 17-fold signal enhancement owing to their synergistic effect, enabling PW@UIO-Au/rGO exhibit high oxidase-like catalytic activity, facilitating their sensing performance. Under optimal experimental conditions, the proposed PW@UIO-Au/rGO ECI-sensor presented excellent sensing performance over a wide range from 0.01 ng mL-1 to 500 ng mL-1 with ultra-low detection of 4.0 pg mL-1. Notably, sensing results in real serum samples were verified by the clinical enzyme-linked immunosorbent assay (ELISA) and electrochemiluminescence immunoassay (ECL) methods with excellent accuracy and consistency, indicating the excellent environmental tolerance of the proposed ECI-sensor. This work provided a promising strategy for designing feasible ultra-sensitive probe for sensing AFP in clinical test.

Surface electric field enhanced biosensor based on symmetrical U-tapered HCF structure for gastric carcinoma biomarker trace detection

In this article, a novel U-tapered hollow-core fiber (HCF) surface plasmon resonance (SPR) biosensor coated with PtS2 for early-stage gastric carcinoma (GC) diagnosis was demonstrated. The article proposed the first investigation to detect Interleukin-10 (IL10) and Interleukin-1β (IL1β) which were associated with the risk of developing gastric carcinoma, using optical fiber SPR technology. Herein, the sensitivity of sensor was effectively improved through a combination of tapered and U-shaped structures. Additionally, to further enhance the detection capability, two-dimensional material PtS2 was utilized to increase the surface electric field intensity of the sensor. Simultaneously, optimization of structural parameters such as taper ratio, bending diameters, and Au film thickness was conducted. Ultimately, the designed sensor achieved a remarkable sensitivity of 13210 nm/RIU within the refractive index (RI) range of 1.33-1.37. The sensor demonstrated exceptional performance, achieving sensitivities of 3.64 nm/(ng/ml) and 7.46 nm/(ng/ml) for the detection of IL10 and IL1β biomarkers, respectively, along with limit of detection (LOD) of 2.74 pg/ml and 1.33 pg/ml, and successfully detecting the presence of these biomarkers in the serum of gastric cancer patients. Overall, the proposed sensor exhibits significant potential in early gastric cancer detection and advances the application of optical fiber SPR sensors in trace biodetection.

From Structure to Application: The Evolutionary Trajectory of Spherical Nucleic Acids

Since the proposal of the concept of spherical nucleic acids (SNAs) in 1996, numerous studies have focused on this topic and have achieved great advances. As a new delivery system for nucleic acids, SNAs have advantages over conventional deoxyribonucleic acid (DNA) nanostructures, including independence from transfection reagents, tolerance to nucleases, and lower immune reactions. The flexible structure of SNAs proves that various inorganic or organic materials can be used as the core, and different types of nucleic acids can be conjugated to realize diverse functions and achieve surprising and exciting outcomes. The special DNA nanostructures have been employed for immunomodulation, gene regulation, drug delivery, biosensing, and bioimaging. Despite the lack of rational design strategies, potential cytotoxicity, and structural defects of this technology, various successful examples demonstrate the bright and convincing future of SNAs in fields such as new materials, clinical practice, and pharmacy.

Cu-MOFs@AuPtNPs nanozyme-based immunosorbent assay for colorimetric detection of alpha-fetoprotein

Accurate detection of tumor biomarkers in blood is crucial for diagnosing and treating tumor disease. In this study, a metal enzyme-linked immunosorbent assay (MeLISA) was fabricated for the ultrasensitive and naked-eye detection of tumor biomarker alpha-fetoprotein (AFP) in clinical serum samples. Herein, novel copper metal-organic frameworks and gold platinum nanoparticle composites (Cu-MOFs@AuPtNPs) were synthesized for the first time by an in situ method, which showed an enormous specific surface area and excellent peroxidase (POx) mimicking properties. Cu-MOFs@AuPtNPs linked with antibodies targeting AFP served as a signal nanoprobe to amplify the detection signal. Additionally, the specificity of MeLISA was significantly enhanced through a conventional antigen-antibody reaction and efficient blocking of non-specific sites with BSA. Under optimal conditions, the sandwich-type MeLISA exhibited a wide range from 0.001 to 1000 ng mL-1 (R2 = 0.997) and a low detection limit of 0.86 pg mL-1 (S/N = 3) with acceptable stability, selectivity, and reproducibility. It is noteworthy that the suggested MeLISA performed exceptionally well in detecting clinical serum samples, which were visible to the naked eye and did not require complex platforms. To sum up, the innovative MeLISA based on Cu-MOFs@AuPtNPs provides an alternative method for early cancer diagnosis, particularly in economically backward areas where simple diagnostic apparatus is extremely desirable.

Structure Remodeling Strategy for Open-Cage NiFe@Fe-bis-PBA with Enhanced Peroxidase-like Activity To Monitor Tumor Markers

The inherent metal elements and structures of Prussian blue analogue (PBA) nanozymes have restricted their enzyme-mimicking activity. Therefore, the rational regulation of PBA nanozymes to improve their catalytic activity is highly desirable for biosensing applications. Herein, we propose a structure remodeling strategy to construct an open-cage Fe PBA-anchored NiFePBA (NiFe@Fe bis-PBA) nanozyme with significantly enhanced enzyme-mimicking activity. The formation process and mechanism for this bis-PBA nanozyme were studied in detail. Specifically, a cubic NiFePBA precursor was first synthesized and modified with polyvinylpyrrolidone (PVP). With the aid of hydrochloric acid, the added potassium ferricyanide was reduced by PVP and re-coordinated on the surface of NiFePBA to form the NiFe@Fe bis-PBA nanozyme with a special open-cage core-shell structure. The resultant NiFe@Fe bis-PBA nanozyme was further exploited to immobilize secondary antibodies, serving as a novel signal probe for developing highly sensitive electrochemical immunosensors for monitoring tumor markers. The constructed electrochemical immunosensor possesses a very wide linear range of 0.005-100 ng/mL and a low detection limit of 0.89 pg/mL for alpha-fetoprotein with high specificity and acceptable reproducibility and stability. This work offers a general and promising strategy for remodeling PBA nanozymes with a very favorable structure and metal element distribution, which enhances their enzyme-mimicking properties for applications in different fields.

Portable Saliva Sensor Based on Dual Recognition Elements for Detection of Caries Pathogenic Bacteria

Dental caries is one of the most common diseases affecting more than 2 billion people's health worldwide. In a clinical setting, it is challenging to predict and proactively guard against dental cavities prior to receiving a confirmed diagnosis. Streptococcus mutans (S. mutans) in saliva has been recognized as the main causative bacterial agent that causes dental caries. High sensitivity, good selectivity, and a wide detection range are incredibly important factors to affect S. mutans detection in practical applications. In this study, we present a portable saliva biosensor designed for the early detection of S. mutans with the potential to predict the occurrence of dental cavities. The biosensor was fabricated using a S. mutans-specific DNA aptamer and S. mutans-imprinted polymers. Methylene blue was utilized as a redox probe in the sensor to generate current signals for analysis. When S. mutans enters complementarily S. mutans cavities, it blocks electron transfer between methylene blue and the electrode, resulting in decreases in the reduction current signal. The signal variations are associated with S. mutans concentrations that are useful for quantitative analysis. The linear detection range of S. mutans is 102-109 cfu mL-1, which covers the critical concentration of high caries risk. The biosensor exhibited excellent selectivity toward S. mutans in the presence of other common oral bacteria. The biosensor's wide detection range, excellent selectivity, and low limit of detection (2.6 cfu mL-1) are attributed to the synergistic effect of aptamer and S. mutans-imprinted polymers. The sensor demonstrates the potential to prevent dental caries.

Smart Stimuli-Responsive Spherical Nucleic Acids: Cutting-Edge Platforms for Biosensing, Bioimaging, and Therapeutics

Spherical nucleic acids (SNAs) with exceptional colloidal stability, multiple modularity, and programmability are excellent candidates to address common molecular delivery-related issues. Based on this, the higher targeting accuracy and enhanced controllability of stimuli-responsive SNAs render them precise nanoplatforms with inestimable prospects for diverse biomedical applications. Therefore, tailored diagnosis and treatment with stimuli-responsive SNAs may be a robust strategy to break through the bottlenecks associated with traditional nanocarriers. Various stimuli-responsive SNAs are engineered through the incorporation of multifunctional modifications to meet biomedical demands with the development of nucleic acid functionalization. This review provides a comprehensive overview of prominent research in this area and recent advancements in the utilization of stimuli-responsive SNAs in biosensing, bioimaging, and therapeutics. For each aspect, SNA nanoplatforms that exhibit responsive behavior to both internal stimuli (including sequence, enzyme, redox reactions, and pH) and external stimuli (such as light and temperature) are highlighted. This review is expected to offer inspiration and guidance strategies for the rational design and development of stimuli-responsive SNAs in the field of biomedicine.

Sandwich-type supersensitive electrochemical aptasensor of glypican-3 based on PrGO-Hemin-PdNP and AuNP@PoPD

A new sandwich-type electrochemical biosensing platform was developed by gold @polyphthalenediamine nanohybrids (AuNP@PoPD) as the sensing platform and phosphorus doped reduced graphene oxide-hemin-palladium nanoparticles (PrGO-Hemin-PdNP) as the signal amplifier for phosphatidylinositol proteoglycan 3 (GPC3). AuNP@PoPD, co-electrodeposited into the screen printed electrode with high conductivity and stability, is dedicated to assembling the primary GPC3 aptamer (GPC3Apt). The second GPC3Apt immobilized on the high conductivity and large surface area of PrGO-Hemin-PdNP was utilized as an electrochemical signal reporter by hemin oxidation (PrGO-Hemin-PdNP-GPC3Apt). In the range 0.001-10.0 ng/mL, the hemin oxidation current signal of the electrochemical aptasensor increased log-linearly with the concentration of GPC3, the lowest detection limit was 0.13 pg/mL, and the sensitivity was 2.073 μA/μM/cm2. The aptasensor exhibited good sensing performance in a human serum sample with the relative error of 4.31-8.07%. The sandwich sensor showed good selectivity and stability for detection GPC3 in human serum samples, providing a new efficient and sensitive method for detecting HCC markers.

Biosensing of Alpha-Fetoprotein: A Key Direction toward the Early Detection and Management of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is currently one of the most prevalent cancers worldwide. Associated risk factors include, but are not limited to, cirrhosis and underlying liver diseases, including chronic hepatitis B or C infections, excessive alcohol consumption, nonalcoholic fatty liver disease (NAFLD), and exposure to chemical carcinogens. It is crucial to detect this disease early on before it metastasizes to adjoining parts of the body, worsening the prognosis. Serum biomarkers have proven to be a more accurate diagnostic tool compared to imaging. Among various markers such as nucleic acids, circulating genetic material, proteins, enzymes, and other metabolites, alpha-fetoprotein (AFP) is a protein marker primarily used to diagnose HCC. However, current methods need a large sample and carry a high cost, among other challenges, which can be improved using biosensing technology. Early and accurate detection of AFP can prevent severe progression of the disease and ensure better management of HCC patients. This review sheds light on HCC development in the human body. Afterward, we outline various types of biosensors (optical, electrochemical, and mass-based), as well as the most relevant studies of biosensing modalities for non-invasive monitoring of AFP. The review also explains these sensing platforms, detection substrates, surface modification agents, and fluorescent probes used to develop such biosensors. Finally, the challenges and future trends in routine clinical analysis are discussed to motivate further developments.

Spherical nucleic acids: emerging amplifiers for therapeutic nanoplatforms

Gene therapy is a revolutionary treatment approach in the 21st century, offering significant potential for disease prevention and treatment. However, the efficacy of gene delivery is often compromised by the inherent challenges of gene properties and vector-related defects. It is crucial to explore ways to enhance the curative effect of gene drugs and achieve safer, more widespread, and more efficient utilization, which represents a significant challenge in amplification gene therapy advancements. Spherical nucleic acids (SNAs), with their unique physicochemical properties, are considered an innovative solution for scalable gene therapy. This review aims to comprehensively explore the amplifying contributions of SNAs in gene therapy and emphasize the contribution of SNAs to the amplification effect of gene therapy from the aspects of structure, application, and recent clinical translation - an aspect that has been rarely reported or explored thus far. We begin by elucidating the fundamental characteristics and scaling-up properties of SNAs that distinguish them from traditional linear nucleic acids, followed by an analysis of combined therapy treatment strategies, theranostics, and clinical translation amplified by SNAs. We conclude by discussing the challenges of SNAs and provide a prospect on the amplification characteristics. This review seeks to update the current understanding of the use of SNAs in gene therapy amplification and promote further research into their clinical translation and amplification of gene therapy.

Construction and bioanalytical applications of poly-adenine-mediated gold nanoparticle-based spherical nucleic acids

Owing to the versatile photophysical and chemical properties, spherical nucleic acids (SNAs) have been widely used in biosensing. However, traditional SNAs are formed by self-assembly of thiolated DNA on the surface of a gold nanoparticle (AuNP), where it is challenging to precisely control the orientation and surface density of DNA. As a new SNA, a polyadenine (polyA)-mediated SNA using the high binding affinity of consecutive adenines to AuNPs shows controllable surface density and configuration of DNA, which can be used to improve the performance of a biosensor. Herein, we first introduce the properties of polyA-mediated SNAs and fundamental principles regarding the polyA-AuNP interaction. Then, we provide an overview of current representative synthesis methods of polyA-mediated SNAs and their advantages and disadvantages. After that, we summarize the application of polyA-mediated SNAs in biosensing based on fluorescence and colorimetric methods, followed by discussion and an outlook of future challenges in this field.

A bimetallic metal-organic framework with high enzyme-mimicking activity for an integrated electrochemical immunoassay of carcinoembryonic antigen

Metal-organic frameworks (MOFs) show excellent catalytic activity and have been widely applied in diagnosis of diseases and tumors. However, current assay methods usually involve cumbersome configurations and complicated procedures, which inhibit their practical applications. Hence, a Cu-Ni MOF/carbon printed electrode (CPE)-based integrated electrochemical immunosensor was constructed for highly sensitive and efficient determination of carcinoembryonic antigen (CEA). First, highly conductive carbon ink was screen-printed onto a polyethylene terephthalate substrate to manufacture a CPE. Afterward, an aminated Cu-Ni MOF was prepared by a typical solvothermal strategy and modified on the CPE. Owing to its excellent peroxidase activity, the Cu-Ni MOF can catalytically oxidize hydroquinone using hydrogen peroxide, which greatly amplifies the peak current signal. Then the formation of an immune complex inhibited the catalytic activity of the MOF, thus enabling the quantitative determination of CEA content with a wide linear range of 0.5 pg mL-1-500 ng mL-1 and a low detection limit of 0.16 pg mL-1. Furthermore, the Cu-Ni MOF/CPE-based integrated portable electrochemical immunosensor also showed satisfactory performance in the detection of CEA in clinical serum samples with excellent accuracy, showing great potential for application in point-of-care disease diagnosis.

The Applications of Electrochemical Immunosensors in the Detection of Disease Biomarkers: A Review

Disease-related biomarkers may serve as indicators of human disease. The clinical diagnosis of diseases may largely benefit from timely and accurate detection of biomarkers, which has been the subject of extensive investigations. Due to the specificity of antibody and antigen recognition, electrochemical immunosensors can accurately detect multiple disease biomarkers, including proteins, antigens, and enzymes. This review deals with the fundamentals and types of electrochemical immunosensors. The electrochemical immunosensors are developed using three different catalysts: redox couples, typical biological enzymes, and nanomimetic enzymes. This review also focuses on the applications of those immunosensors in the detection of cancer, Alzheimer's disease, novel coronavirus pneumonia and other diseases. Finally, the future trends in electrochemical immunosensors are addressed in terms of achieving lower detection limits, improving electrode modification capabilities and developing composite functional materials.