An electrochemical immunosensor for ultrasensitive detection of carbohydrate antigen 199 based on Au@Cu(x)OS yolk-shell nanostructures with porous shells as labels

Nanochannel confined graphene quantum dots/platinum nanoparticles boosts electrochemiluminescence of luminal-O2 system for sensitive immunoassay

Sensitive detection of tumor biomarkers is of great significance for early cancer diagnosis, treatment evaluation, and recurrence monitoring. Development of convenient electrochemiluminescence (ECL) immunosensor using dissolved oxygen (O2) as an endogenous co-reactant of luminol combined with efficient nanocatalysts to boost ECL signal in neutral media is highly desirable. Herein, sensitive detection of tumor biomarker using ECL of luminal-O2 enhanced by confinement of nitrogen-doped graphene quantum dots (N-GQDs) and platinum nanoparticles (PtNPs) on nanochannel array was demonstrated. A high-density nanochannel array-modified electrode was achieved by rapidly growing an amino-functionalized. Vertically-ordered mesoporous silica film (NH2-VMSF) on the inexpensive and readily available indium tin oxide (ITO) electrode. Through simple electrodeposition, N-GQDs were confined and PtNPs were in-situ synthesized in nanochannels of NH2-VMSF. These confined nanocomposites catalyzed the electroreduction of O2 at negative potentials to generate a large amount of reactive oxygen species (ROS) and facilitated luminol oxidation, enhancing the ECL signal of luminol by 25 times. Two immunosensors were fabricated after covalent immobilization of the recognition antibody of carbohydrate antigen 199 (CA199) or carbohydrate antigen 125 (CA125) on the outer surface of the NH2-VMSF and blocking of non-specific sites. When tumor biomarkers bind to the corresponding antibodies on the recognition interface, the formed immunocomplex hindered the diffusion of luminol to the underlying electrode, resulting in a decrease in the ECL signal and sensitive detection of tumor biomarker. The constructed CA199 immunosensor exhibited a linear detection range for CA199 from 0.5 mU mL-1 to 50 U mL-1, with a detection limit (DL) of 0.03 mU mL-1. For CA125 detection, linear detection ranged from 0.5 mU mL-1 to 500 U mL-1, with a DL of 0.005 mU mL-1. The fabricated immunosensors demonstrated good selectivity and high reproducibility. This study provides great potential for the development of efficient luminol ECL systems in neutral media and expands the biological application in sensitive detection of tumor biomarker.

A simple electrochemical strategy for the detection of the cancer marker CA19-9 by signal amplification using copper organic framework nanocomposite

In this work, label-free electrochemical immunosensing of the cancer biomarker carbohydrate antigen 19-9 (CA19-9) is reported using [Fe(CN)6]3-/4- as a signal probe and a copper organic framework (Cu-BTC) nanocomposite for the amplification of the signal. The immunosensor was fabricated by the following process. First, the Cu-BTC nanomaterial with a larger surface area and good biocompatibility was synthesized to improve the dispersion of gold nanoparticles (Au NPs). Then, nitrogen-doped graphene (N-GR) was combined with Cu-BTC to form the nanocomposite. The synthesized Cu-BTC@N-GR@AuNPs@CS nanocomposite was employed to modify the surface of the immunosensor to accelerate the electron transfer rate and improve the immobilization amount of CA19-9 antibodies (Ab). Various techniques, including TEM, SEM and XPS were used to characterize Cu-BTC and nanocomposites. Differential pulse voltammetry (DPV) was used to measure the electrochemical response of the immunosensor in [Fe(CN)6]3-/4-. The signal intensity of the immunosensor was linearly changed upon increasing the concentration of CA19-9 antigen from 10 μU mL-1 to 100 U mL-1, and a detection limit of 4.2 μU mL-1 was achieved. Furthermore, the immunosensor showed good stability, reproducibility and specificity, indicating its potential application in clinical analysis.

Efficient Simultaneous Detection of Metabolites Based on Electroenzymatic Assembly Strategy

Objective and Impact Statement: We describe an electroenzymatic mediator (EM) sensor based on an electroenzymatic assembly peak separation strategy, which can efficiently realize the simultaneous detection of 3 typical cardiovascular disease (CVD) metabolites in 5 μl of plasma under one test. This work has substantial implications toward improving the efficiency of chronic CVD assessment. Introduction: Monitoring CVD of metabolites is strongly associated with disease risk. Independent and time-consuming detection in hospitals is unfavorable for chronic CVD management. Methods: The EM was flexibly designed by the cross-linking of electron mediators and enzymes, and 3 EM layers with different characteristics were assembled on one electrode. Electrons were transferred under tunable potential; 3 metabolites were quantitatively detected by 3 peak currents that correlated with metabolite concentrations. Results: In this study, the EM sensor showed high sensitivity for the simultaneous detection of 3 metabolites with a lower limit of 0.01 mM. The linear correlation between the sensor and clinical was greater than 0.980 for 242 patients, and the consistency of risk assessment was 94.6%. Conclusion: Metabolites could be expanded by the EM, and the sensor could be a promising candidate as a home healthcare tool for CVD risk assessment.

Simple synthesis of PtRu nanoassemblies as signal amplifiers for electrochemical immunoassay of carbohydrate antigen 19-9

In clinical analysis, carbohydrate antigen 19-9 (CA199) is a gold standard for pancreatic cancer diagnosis. Herein, PtRu nanoassemblies (NAs) were synthesized via a facile one-step solvothermal approach, with the help of octylphenoxypolye thoxyethanol (NP-40) acted as a growth-directing molecule, and triethylene glycol (TEG) worked as a reductant and solvent. During the assembly process of small particles, a large number of voids were formed, which significantly increase the specific surface area of the PtRu NAs exhibiting excellent electrocatalytic performance. Incorporating the PtRu NAs as signal amplifiers for potassium ferrocyanide oxidation into the specific molecular recognition of proteins, a facile signal-enhanced electrochemical (EC) immunosensor was developed. Verified by a series of experiments, the proposed immunosensor presented a wide linear range (10^-4-70 U mL^-1) and a low detection limit (3.3 × 10^-5 U mL^-1), accompanied by good reproducibility, selectivity, and stability, which could be applied in human serum samples for the determination of CA199, and was comparable to commercial electrochemiluminescence (ECL) immunoassay. Feasibility of batch fabrication of PtRu NAs makes nanomaterial-based EC immunoassay promising for the determination of similar cancer markers in future.

Electrochemical biosensors for measurement of colorectal cancer biomarkers

Colorectal cancer (CRC) is associated with one of the highest rates of mortality among cancers worldwide. The early detection and management of CRC is imperative. Biomarkers play an important role in CRC screening tests, CRC treatment, and prognosis and clinical management; thus rapid and sensitive detection of biomarkers is helpful for early detection of CRC. In recent years, electrochemical biosensors for detecting CRC biomarkers have been widely investigated. In this review, different electrochemical detection methods for CRC biomarkers including immunosensors, aptasensors, and genosensors are summarized. Further, representative examples are provided that demonstrate the advantages of electrochemical sensors modified by various nanomaterials. Finally, the limitations and prospects of biomarkers and electrochemical sensors in detection are also discussed. Graphical abstract.

A three-dimensional CoNi-MOF nanosheet array-based immunosensor for sensitive monitoring of human chorionic gonadotropin with core-shell ZnNi-MOF@Nile Blue nanotags

A CoNi-based metal-organic framework (CoNi-MOF) nanosheet array is synthesized by the treatment of a CoNi layered double hydroxide nanosheet array on Ni foam with 3,5-diaminobenzoic acid. The CoNi-MOF nanosheet array with amino and carboxyl groups can be used to capture the human chorionic gonadotropin (HCG) primary antibody (HCG Ab1). Nile Blue decorated ZnNi-MOF (NB@ZnNi-MOF) spheres immobilized with HCG secondary antibodies (HCG Ab2) are used for signal amplification. When HCG exists in an analytical sample, a sandwich structure is formed and an electrochemical signal is produced. The analytical signal generated during the detection is caused by the conversion of Co(ii) and Co(iii) in the CoNi-MOF nanosheet array. The Nile Blue of the NB@ZnNi-MOF sphere, as a kind of redox-active species, is responsible for the electrochemical signal amplification in the immunosensor. On the basis of the above advantages, the HCG immunosensor exhibits a lower limit of detection (1.85 × 10-3 mIU mL-1) and a wide linear range from 0.005 mIU mL-1 to 250 mIU mL-1. Additionally, this immunosensor is used to quantitatively detect HCG in human blood serum and shows good correlations with the standard enzyme-linked immunosorbent assay (ELISA), providing a high value on clinical diagnosis.

Copper peroxide/ZIF-8 self-producing H2O2 triggered cascade reaction for amperometric immunoassay of carbohydrate antigen 19-9

Generally, H₂O₂ is frequently adopted to improve analysis capabilities of various detection systems. However, the addition of H₂O₂ with relatively higher concentration can lower the bioactivity of antibodies or antigens and the sensing interface stability in most peroxidase and peroxidase-like immunosensors. In order to solve these issues, we designed a novel copper peroxide/ZIF-8 immunoprobe that can self-produce H₂O₂ to trigger a cascade reaction for the sensitive detection of carbohydrate antigen 19-9. Specifically, CP/ZIF-8 plays a key role as a "signal switch" in the immunosensor. In the presence of HCl, the structures of ZIF-8 and copper peroxide can be broken, producing Cu²⁺ and H₂O₂ and a subsequent Fenton-type reaction that generates •OH. The resulting •OH can induce the decomposition of 3-aminobenzeneboronic acid/poly (vinyl alcohol) (PVA) film on the electrode. Although the immunosensor initially showed little current signal due to the poor conductivity pf ZIF-8 and PVA, the current signal was significantly amplified by a HCl-triggered cascade reaction. Under optimal conditions, the immunosensor displayed a wide linear range from 0.0001 to 100 U mL^-1 with an ultralow limit of detection of 53.5 μU mL^-1 (S/N = 3) for carbohydrate antigen 19-9. Considering these advantages, namely self-producing H₂O₂ and easy operation, this strategy paves a new way to design other novel sensors.

Combined Detection of CA19-9 and MUC1 Using a Colorimetric Immunosensor Based on Magnetic Gold Nanorods for Ultrasensitive Risk Assessment of Pancreatic Cancer

We herein report a facile approach for developing an enzyme-free colorimetric immunosensor based on a magnetic iron oxide (IO)-coated gold nanorod (MGNR) nanocomposite with high electron transfer ability to accelerate the color bleaching reaction of methyl orange (MO) in the presence of NaBH₄ for ultrasensitive detection of cancer antigens. In the case of MO, the reaction rate of MGNRs showed approximately 45.6-fold and 1520.8-fold higher than that of Cys-GNRs and NaBH₄, respectively. The proposed colorimetric immunosensor was demonstrated to enable simple, cost-effective, sensitive, and specific carbohydrate antigen 19-9 (CA19-9) and mucin 1 (MUC1) detection for risk evaluation of pancreatic cancer (PC) with a small volume of serum sample without the use of any enhancing solutions or enzymes. By increasing the concentration of CA19-9 and MUC1, more MGNRs remained in the plate well to enhance the color bleaching of MO. As a proof-of-concept, the limit of detection (LOD) of 3.5 × 10^-5 U/mL for CA19-9 and 5.2 × 10^-6 U/mL for MUC1 was obtained with a wide linear quantification range from 8.6 × 10^-5 U/mL to 1.4 × 10^-2 U/mL for CA19-9 and 1.3 × 10^-5 U/mL to 2.1 × 10^-3 U/mL for MUC1, suggesting potential clinical applications for the early risk evaluation of PC.

Biosensors for early diagnosis of pancreatic cancer: a review

Pancreatic cancer is characterized by extremely high mortality and poor prognosis and is projected to be the leading cause of cancer deaths by 2030. Due to the lack of early symptoms and appropriate methods to detect pancreatic carcinoma at an early stage as well as its aggressive progression, the disease is often quite advanced by the time a definite diagnosis is established. The 5-year relative survival rate for all stages is approximately 8%. Therefore, detection of pancreatic cancer at an early surgically resectable stage is the key to decrease mortality and to improve survival. The traditional methods for diagnosing pancreatic cancer involve an imaging test, such as ultrasound or magnetic resonance imaging, paired with a biopsy of the mass in question. These methods are often expensive, time consuming, and require trained professionals to use the instruments and analyze the imaging. To overcome these issues, biosensors have been proposed as a promising tool for the early diagnosis of pancreatic cancer. The present review critically discusses the latest developments in biosensors for the early diagnosis of pancreatic cancer. Protein and microRNA biomarkers of pancreatic cancer and corresponding biosensors for pancreatic cancer diagnosis have been reviewed, and all these cases demonstrate that the emerging biosensors are becoming an increasingly relevant alternative to traditional techniques. In addition, we discuss the existing problems in biosensors and future challenges.

Label-assisted chemical adsorption triggered conversion of electroactivity of sensing interface to achieve the Ag/AgCl process for ultrasensitive detection of CA 19-9

Efficient strategies in enhancing sensitivity are pivotal to ultrasensitive detection of tumor markers. In this work, based on the strategy of label-assisted chemical adsorption triggered conversion of electroactivity of sensing interface, a Ag/AgCl process was achieved to enhance sensitivity of the constructed sandwich-type amperometric immunosensor for ultrasensitive detection of carbohydrate antigen 19-9 (CA19-9). Briefly, polydopamine-Ag nanoparticles (PDA-Ag NPs), as signal precursor, combined with labeling antibody were served as labels and graphene oxide-melamine (GO-MA) substrate with chemical absorption capacity was applied as smart sensing interface. After successfully incubating labels, there was primitively no current response due to the poor conductivity between labels and electrode. However, in the presence of H₂O₂, Ag NPs from labels can be etched into Ag ions, which were adsorbed by GO-MA to form GO-MA-Ag as electroactive substrate. Then, the substrate exhibited a sharp and stable electrochemistry peak of solid-state Ag/AgCl process in the buffer containing KCl. The sensitivity toward detection of CA19-9 was notably enhanced based on the appearance of sharp peak. Under optimum conditions, the designed immunosensor demonstrated a wide working range from 0.0001 to 100 U mL^-1 and an ultralow detection limit 0.032 mU mL^-1. Thus, utilizing this strategy to construct immunosensor was highly promising in clinical diagnosis for ultrasensitive detection of tumor makers.

Three dimensional sea-urchin-like PdAuCu nanocrystals/ferrocene-grafted-polylysine as an efficient probe to amplify the electrochemical signals for ultrasensitive immunoassay of carcinoembryonic antigen

A novel sandwich-like immunosensor was efficiently fabricated for detection of carcinoembryonic antigen (CEA) with three dimensional sea-urchin-like PdAuCu nanocrystals (PdAuCu NCs)/ferrocene-grafted-polylysine (Fc-g-PLL) as the label of secondary antibodies (Ab₂) and Au nanoparticles (Au NPs) as the substrate material. Herein, PdAuCu NCs were directly synthesized with polyethylene oxide (PEO) as a growth-directing agent by a facile one-step aqueous method without any organic solvent. Meanwhile, Fc-g-PLL was obtained by covalent linkage of Fc with PLL via Schiff-base reaction. The well-dispersed PdAuCu NCs by Fc-g-PLL have the enlarged surface area, enhanced catalytic properties and superior biocompatibility to amplify the current signals. The resultant immunosensor shows linear relationship of the electrochemical responses with the CEA concentrations within a broader linear range (0.001-100.0 ng mL^-1) and a lower detection limit (0.23 pg mL^-1, S/N = 3). Furthermore, the immunosensor was explored for practical assay of CEA in human serum samples with accredited results. The novel immunoassay provides a feasible platform for early medical diagnosis.

A novel DNA sensor based on C60NPs-PAMAM-PtPNPs to detect VKORC1 gene for guiding rational clinical therapy with warfarin

Reports have indicated that warfarin is the most widely prescribed anticoagulant. However, traditionally prescribed doses for each patient may be too low or too high. The therapeutic effect is often hindered by a lack of evidence-based medical information. Herein, our aim is to provide this information. To accomplish this challenge, we report the development of a novel assay based on biotinylated tetrahedral DNA as a capture probe and fullerene (C₆₀)-based nanomaterial as a redox probe using an ultrasensitivity assay with the Vitamin K epoxide reductase complex, subunit 1 (VKORC1). Platinum porous nanoparticles (PtPNPs) were modified on amino-terminated polyamidoamine (PAMAM)-functionalized C₆₀ nanoparticles (C₆₀NPs). The resultant C₆₀NPs-PAMAM-PtPNPs were used as a redox probe. In this design, C₆₀ exhibited excellent redox activity that was triggered by tetraoctylammonium bromide (TOAB). To improve the immobilization of the tetrahedral DNA capture probe, avidin was introduced during the fabrication of the biosensor because it can provide more active sites for the immobilization capture probe. The free-standing probe on top of the tetrahedral DNA served as a receptor to hybridize with target DNA directly. Different pulse voltammetry (DPV) was applied to record the electrochemical signals, which increased linearly with the target DNA. Under optimal conditions, the prepared biosensor showed a wide linear relationship, from 1 pM to 10 nM, with detection limits of 0.33 pM. This strategy demonstrates a new avenue for the determination of tumour-related mutated nucleotides in biosamples.

Multifunctional Yolk-Shell Nanostructure as a Superquencher for Fluorescent Analysis of Potassium Ion Using Guanine-Rich Oligonucleotides

The excellent performance of a biosensor generally depends on the high signal-to-noise ratio, and the superquencher plays a dominant role in fluorescent sensors. Novel nanoquenchers exhibited high quenching efficiency in various fluorescent assays of biological/chemical molecules. Here, we developed a novel nano-biosensor using Fe₃O₄@C yolk-shell nanoparticles (YSNPs) and studied their quenching effect. We found Fe₃O₄@C YSNP was a superquencher and exhibited an ultrastrong quenching ability, up to almost 100% quenching efficiency, toward fluorophores. Also, Fe₃O₄@C YSNPs possessed the most superior fluorescence restoration efficiency, due to biomolecular recognition event, compared to the other nanoquenchers, including bare Fe₃O₄ NPs, graphene oxide (GO), and single-wall carbon nanotubes (SWCNTs). On the basis of that, a fluorescent sensing platform for potassium-ion (K⁺) analysis with guanine (G)-rich oligonucleotides was designed. As a result, Fe₃O₄@C YSNP-based fluorescent sensors demonstrated excellent performance, with an ultrahigh sensitivity of a detection limit as low as 1.3 μM, as well as a wide dynamic range from 50 μM to 10 mM. The proposed method is fast, simple, and cost-effective, suggesting the great potential for practical applications in biomedical detection and clinical diagnosis.

An ultrasensitive multi-walled carbon nanotube–platinum–luminol nanocomposite-based electrochemiluminescence immunosensor

An ultrasensitive electrochemiluminescence (ECL) immunosensor for carbohydrate antigen 19-9 (CA19-9) detection using multi-walled carbon nanotube–platinum–luminol nanocomposites (MWCNT–Pt–luminol) as nanointerface and signal tags was designed.

Application of APTES-Anti-E-cadherin film for early cancer monitoring

Cancer staging is a way to classify cancer according to the extent of the disease in the body. The stage is usually determined by several factors such as the location of the primary tumor, the tumor size, the degree of spread in the surrounding tissues, etc. The study of E-cadherin (EC) expression on cancerous cells of patients has revealed variations in the molecular expression patterns of primary tumors and metastatic tumors. The detection of these cells requires a long procedure involving conventional techniques, thus, the requirement for development of new rapid devices that permit direct and highly sensitive detection stimulates the sensing field progress. Here, we explore if E-cadherin could be used as a biomarker to bind and detect epithelial cancer cells. Hence, the sensitive and specific detection of E-cadherin expressed on epithelial cells is approached by immobilizing anti-E-cadherin antibody (AEC) onto aminosilanized indium-tin oxide (ITO) surface. The immunosensing surfaces have been characterized by electrochemical measurements, wettability and confocal microscopy and their performance has been assessed in the presence of cancer cell lines. Under optimal conditions, the resulting immunosensor displayed a selective detection of E-cadherin expressing cells, which could be detected either by fluorescence or electrochemical techniques. The developed immunosensing surface could provide a simple tool that can be applied to cancer staging.

An ultrasensitive sandwich-type electrochemical immunosensor based on functionalized mesoporous carbon for IgG detection

Immunoglobulin (IgG) plays an important role in the accurate diagnosis of some diseases.

A Novel Point-of-Care Biomarker Recognition Method: Validation by Detecting Marker for Diabetic Nephropathy

Biological fluid collection to identify and analyze different disease markers is a routine and normal procedure in health care settings. Body fluids are as varied as urine, blood, mucus, cerebrospinal fluid (CSF), tears, semen, etc. The volumes of the collected fluids range from micro liters (e.g., tears, CSF) to tens and hundreds of milliliters (blood, urine, etc.). In some manifestations, a disease marker (particularly protein markers) can occur in trace amounts, yet the fluids collected are in large volumes. To identify these trace markers, cumbersome methods, expensive instruments, and trained personnel are required. We developed an easy method to rapidly capture, concentrate, and identify protein markers in large volumes of test fluids. This method involves the utilization of two antibodies recognizing two different epitopes of the protein biomarker. Antibody-1 helps to capture and concentrate the biomarker and Antibody-2 adsorbed or conjugated to nanogold beads will detect the biomarker. This method was validated in capturing and detecting lipocalin type prostaglandin-D2 synthase, a marker in urine that implicates diabetic nephropathy. A one-step collection, concentration, and detection device was designed based on this method. This device can replace many of the normal body fluid collection devices such as tubes and containers. A one-step fluid collection and biomarker capture and concentration device for rapid diagnosis of diseases has tremendous advantage in terms of cost and providing timely results.

Sensitive electrochemical immunoassay with signal enhancement based on nanogold-encapsulated poly(amidoamine) dendrimer-stimulated hydrogen evolution reaction

A new electrochemical immunosensor with signal enhancement was designed for sensitive detection of disease-related protein (human carbohydrate antigen 19-9, CA 19-9 used in this case).

A label-free amperometric immunosensor for the detection of carcinoembryonic antigen based on novel magnetic carbon and gold nanocomposites

In this work, a novel label-free electrochemical immunosensor was developed for the quantitative detection of carcinoembryonic antigen (CEA).

Immunosensor for prostate-specific antigen using Au/Pd@flower-like SnO2 as platform and Au@mesoporous carbon as signal amplification

The illustration for the constructed electrochemical immunosensor and the signal amplification strategy.

An ultrasensitive electrochemical immunosensor for the detection of CD146 based on TiO2 colloidal sphere laden Au/Pd nanoparticles

An ultrasensitive electrochemical immunosensor was developed for detecting CD146. rGO-TEPA enhanced the loading capacity of Ab₁ and facilitated the electron transfer. Au and Pd nanoparticles on the TiO₂ colloidal sphere facilitated the decomposition of H₂O₂. The immunosensor exhibited an extremely low detection limit of 1.6 pg mL⁻¹ for CD146.

A label-free electrochemical immunosensor with a novel signal production and amplification strategy based on three-dimensional pine-like Au–Cu nanodendrites

A simple and novel label-free electrochemical immunosensor based on a bimetallic alloy was fabricated in this work.

Rapidly accomplished femtomole soluble CD40 ligand detection in human serum: a “green” homobifunctional agent coupled with reduced graphene oxide-tetraethylene pentamine as platform

A reliable and sensitive electrochemical immunosensor based on a “green” conjunction agent coupled with an amino-group qualified material was used for the analysis of soluble CD40 ligand.

Glycan-based diagnostic devices: current progress, challenges and perspectives

The development of glycan-based diagnostic devices is illustrated with recent examples from both carbohydrate recognition and device design aspects.