Multiplexed sandwich immunoassays using flow-injection electrochemiluminescence with designed substrate spatial-resolved technique for detection of tumor markers

Tumor diagnosis using carbon-based quantum dots: Detection based on the hallmarks of cancer

Carbon-based quantum dots (CQDs) have been shown to have promising application value in tumor diagnosis. Their use, however, is severely hindered by the complicated nature of the nanostructures in the CQDs. Furthermore, it seems impossible to formulate the mechanisms involved using the inadequate theoretical frameworks that are currently available for CQDs. In this review, we re-consider the structure-property relationships of CQDs and summarize the current state of development of CQDs-based tumor diagnosis based on biological theories that are fully developed. The advantages and deficiencies of recent research on CQDs-based tumor diagnosis are thus explained in terms of the manifestation of nine essential changes in cell physiology. This review makes significant progress in addressing related problems encountered with other nanomaterials.

Dual-potential encoded electrochemiluminescence for multiplexed gene assay with one luminophore as tag

Multiplexed gene assay for simultaneously detecting the multi-targets of nucleic acids is strongly anticipated for the accurate diseases diagnosis and prediction, and all commercial available gene assays for IVD are a kind of single-target assay. Herein, a dual-potential encoded and coreactant-free electrochemiluminescence (ECL) strategy is proposed for the multiplexed gene assay, which can be conveniently carried out by directly oxidizing the same luminescent tag of dual-stabilizers-capped CdTe nanocrystals (NCs). The CdTe NCs linked with sulfhydryl-RNA via Cd-S bond merely exhibits one ECL process around 0.32 V with a narrow triggering-potential-window of 0.35 V, while CdTe NCs linked with amino-RNA via amide linkage solely gives off one ECL process around 0.82 V with a narrow triggering-potential-window of 0.30 V. Multiplexing ECL of both sulfhydryl-RNA-functionalized CdTe NCs and amino-RNA-functionalized CdTe NCs can be utilized to simultaneously detect the open reading frame 1ab (ORF1ab) and the nucleoprotein (N) genes without crosstalk, in which ECL of sulfhydryl-RNA-functionalized CdTe NCs can dynamically determine ORF1ab from 200 aM to 10 fM with a limit of detection (LOD) of 100 aM, while ECL of amino-RNA-functionalized CdTe NCs can linearly detect N gene from 5 fM to 1 pM with a LOD of 2 fM. Post-engineering CdTe NCs with RNA in a labeling-bond engineering way would provide a potential-selective and encoded ECL strategy for multiplexed gene assay with one luminophore.

Effective voltammetric tool for simultaneous detection of MMP-1, MMP-2, and MMP-9; important non-small cell lung cancer biomarkers

Simultaneous detection of multiple biomarkers can allow to reduce the costs of medical diagnostics, and thus improve the accuracy and effectiveness of disease diagnosis and prognosis. Here, for the first time, we present a low-cost, simple, and rapid method for simultaneous detection of three matrix metalloproteinases (MMP-1, MMP-2, and MMP-9) that play important roles in the progression of lung cancer. The sensor matrix was constructed using a G2 polyamidoamine dendrimer (PAMAM) containing amino, carboxyl, and sulfhydryl groups. The recognition process was based on specific enzymatic cleavage of the Gly-Ile peptide bond by MMP-1, Gly-Leu bond by MMP-2, and Gly-Met bond by MMP-9, and monitoring was done by square wave voltammetry. The activity of metalloproteinases was detected based on the change of current signals of redox receptors (dipeptides labeled with electroactive compounds) covalently anchored onto the electrode surface. The conditions of the biosensor construction, including the concentration of receptors on the sensor surface and the time of interaction of the receptor with the analyte, were carefully optimized. Under optimal conditions, the linear response of the developed method ranged from 1.0⋅10^-8 to 1.0 mg⋅L^-1, and the limit of detection for MMP-1, MMP-2, and MMP-9 was 0.35, 0.62, and 1.10 fg⋅mL^-1, respectively. The constructed biosensor enabled us to efficiently profile the levels of active forms of MMP-1, MMP-2, and MMP-9 in tissue samples (plasma and lung and tumor extracts). Thus, the developed biosensor can aid in the early detection and diagnosis of lung cancer.

Electrochemical Signal Substance for Multiplexed Immunosensing Interface Construction: A Mini Review

Appropriate labeling method of signal substance is necessary for the construction of multiplexed electrochemical immunosensing interface to enhance the specificity for the diagnosis of cancer. So far, various electrochemical substances, including organic molecules, metal ions, metal nanoparticles, Prussian blue, and other methods for an electrochemical signal generation have been successfully applied in multiplexed biosensor designing. However, few works have been reported on the summary of electrochemical signal substance applied in constructing multiplexed immunosensing interface. Herein, according to the classification of labeled electrochemical signal substance, this review has summarized the recent state-of-art development for the designing of electrochemical immunosensing interface for simultaneous detection of multiple tumor markers. After that, the conclusion and prospects for future applications of electrochemical signal substances in multiplexed immunosensors are also discussed. The current review can provide a comprehensive summary of signal substance selection for workers researched in electrochemical sensors, and further, make contributions for the designing of multiplexed electrochemical immunosensing interface with well signal.

Microfluidic Flow Injection Immunoassay System for Algal Toxins Determination: A Case of Study

A novel flow injection microfluidic immunoassay system for continuous monitoring of saxitoxin, a lethal biotoxin, in seawater samples is presented in this article. The system consists of a preimmobilized G protein immunoaffinity column connected in line with a lab-on-chip setup. The detection of saxitoxin in seawater was carried out in two steps: an offline incubation step (competition reaction) performed between the analyte of interest (saxitoxin or Ag, as standard or seawater sample) and a tracer (an enzyme-conjugated antigen or Ag*) toward a specific polyclonal antibody. Then, the mixture was injected through a “loop” of a few μL using a six-way injection valve into a bioreactor, in line with the valve. The bioreactor consisted of a small glass column, manually filled with resin upon which G protein has been immobilized. When the mixture flowed through the bioreactor, all the antibody-antigen complex, formed during the competition step, is retained by the G protein. The tracer molecules that do not interact with the capture antibody and protein G are eluted out of the column, collected, and mixed with an enzymatic substrate directly within the microfluidic chip, via the use of two peristaltic pumps. When Ag* was present, a color change (absorbance variation, ΔAbs) of the solution is detected at a fixed wavelength (655 nm) by an optical chip docking system and registered by a computer. The amount of saxitoxin, present in the sample (or standard), that generates the variation of the intensity of the color, will be directly proportional to the concentration of the analyte in the analyzed solution. Indeed, the absorbance response increased proportionally to the enzymatic product and to the concentration of saxitoxin in the range of 3.5 × 10^–7–2 × 10^–5 ng ml⁻¹ with a detection limit of 1 × 10^–7 ng ml⁻¹ (RSD% 15, S N⁻¹ equal to 3). The immunoanalytical system has been characterized, optimized, and tested with seawater samples. This analytical approach, combined with the transportable and small-sized instrumentation, allows for easy in situ monitoring of marine water contaminations.

A universal assay strategy for sensitive and simultaneous quantitation of multiplex tumor markers based on the stirring rod-immobilized DNA-LaMnO3 perovskite-metal ions encoded probes

It was extremely urgent to develop some simultaneous and sensitive biosensors for detecting multiplex serum tumor markers (TMs) for early screening of cancers. Herein, a multiplex assay was developed based on the DNA-LaMnO₃ (DNA-LMO) perovskite encoded probes and targets mediated competitive replacement strategy. Alpha fetoprotein (AFP), carcinoembryonic antigen (CEA) and prostate specific antigen (PSA) markers were employed as representative target TMs. Aptasensor is prepared by a series of DNA-LMO-M encode probes which were prepared by three hyperbranched DNA firstly immobilized on LMO encapsulating Pb, Cd or Cu ions. Then, three TMs aptamers were labeled on the stirring-rod and hybridized with the probes. After the developed encoded probes was incubated the TMs, the encoded probes corresponding to different TMs can be released into the supernatant through the competitive replacement. The inner metal ion can be simultaneously detected by square wave voltammetry corresponding to various TMs. Since the stirring rod can enrich many encoded probes containing a lot of metal ions, multiplex signal amplification can be realized. Due to the enrichment and easy separation of the stirring rod, the signal-to-noise ratio was also obviously improved and thus to results in good sensitivity and accuracy. Moreover, it took only 20 min to detect three targets which much faster than many same types of aptasensor. Under the optimal conditions, the low detection limit for CEA (3.6 × 10^-4 ng/mL), AFP (3.4 × 10^-4 ng/mL) and PSA (2.8 × 10^-4 ng/mL) were obtained. Therefore, this method is likely to be used for early and sensitive screening of tumors.

Recent developments in electrochemiluminescence nanosensors for cancer diagnosis applications

In recent years, electrochemiluminescence (ECL) nanosensing systems have undergone rapid development and made significant progress in ultrasensitive analysis and cell imaging. Because of the unique advantages of high selectivity, ultra-sensitivity, and good reproducibility, ECL nanosensors can open new paths for cancer diagnosis. With the development of ECL nanosensors, high-throughput analysis, visual detection and spatially resolved ECL imaging of single cells are being realized. The innovations of ECL nanosensors consist of electrochemical excitation, coreactant catalysis, light radiation and luminescence signal amplification, which involve several fields such as nanotechnology, catalysis, optics, and electrochemistry. The developments of ECL instruments also relate to imaging technology. Herein, we review the construction modes, sensing strategies and cancer diagnosis applications of ECL nanosenors. Firstly, the nano-components of the ECL sensing system are discussed. The construction and signal amplification methods of the nanosensing system are emphasized. Secondly, the high-efficiency cancer identification strategies are presented, including protein tumor marker detection, nucleic acid assay, cancer cell identification and exosome detection. The recent advances in representative examples of ECL nanosenors in cancer diagnosis are highlighted, including high-throughput ECL analysis, in situ assay, visual ECL detection, single-cell imaging diagnosis, and so on. Finally, the challenges are featured based on the recent development of the ECL nanosensing system in the clinical diagnosis. The ECL nanosensors provide effective and reliable analytical methods and open new paths for cancer diagnosis. It is noteworthy that the prospects of the ECL nanosensing system in clinical diagnosis are instructive to the developments of other nanosensor research.

An ultrasensitive immunosensor based on manganese dioxide-graphene nanoplatelets and core shell Fe3O4@Au nanoparticles for label-free detection of carcinoembryonic antigen

A novel electrochemical immunosensor was developed for label-free detection of carcinoembryonic antigen (CEA) as a cancer biomarker. The designed immunosensor was based on CEA antibody (anti-CEA) anchored with core shell Fe₃O₄@Au nanoparticles which were immobilized on a screen-printed carbon electrode modified with manganese dioxide decorating on graphene nanoplatelets (SPCE/GNP-MnO₂/Fe₃O₄@Au-antiCEA). The SPCE was placed onto a home-made electrode holder for easy handling. The approach was based on direct binding of CEA to a fixed amount of anti-CEA on the modified electrode for the specific detection using linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) monitored in a solution containing 5 mM [Fe(CN)₆^3-/4-] prepared in 0.1 M phosphate buffer at pH 7.4. The difference in signal response owing to the redox reaction of [Fe(CN)₆]^3-/4- before and after interaction with CEA was regarded as the immunosensor response corresponding directly to the CEA concentration. Under optimized conditions, the linear range of 0.001-100 ng/mL, and the detection limits of 0.10 pg/mL (LSV) and 0.30 pg/mL (EIS) were evaluated. The applicability of the immunosensor was verified by well-corresponding determination of CEA in diluted human serum samples by electrochemiluminescence (ECL) immunoassay. Therefore, the proposed immunosensor could be suitable enough for a real sample analysis of CEA.

Hierarchically structured microchip for point-of-care immunoassays with dynamic detection ranges

Point-of-care (POC) medical assays provide critical information to guide clinical therapy for a broad range of medical scenarios, such as resource-poor settings and specialty departments in hospitals. Even though many types of POC assays can be done in automated devices, these POC assays typically cannot well accommodate the multiplexed detection of biomarkers where a large dynamic range is needed. Here, we report a POC assay, which is both automated and suitable for detecting multiple biomarkers with dynamic detection ranges. We call it a dynamic multiplexed immunoassay (DMI). We control the concentrations of capture antibodies and the intensity of the readout signal to dynamically modulate the detection range of immunoassays (pg mL^-1 to μg mL^-1), leading to the multiplexed detection of C-reactive protein (CRP), procalcitonin (PCT), and interleukin 6 (IL-6) simultaneously in undiluted human serum samples. The POC assay allows the rapid and accurate detection of infection in patients.

A Stroke Risk Detection: Improving Hybrid Feature Selection Method

Background

Stroke is one of the most common diseases that cause mortality. Detecting the risk of stroke for individuals is critical yet challenging because of a large number of risk factors for stroke.

Objective

This study aimed to address the limitation of ineffective feature selection in existing research on stroke risk detection. We have proposed a new feature selection method called weighting- and ranking-based hybrid feature selection (WRHFS) to select important risk factors for detecting ischemic stroke.

Methods

WRHFS integrates the strengths of various filter algorithms by following the principle of a wrapper approach. We employed a variety of filter-based feature selection models as the candidate set, including standard deviation, Pearson correlation coefficient, Fisher score, information gain, Relief algorithm, and chi-square test and used sensitivity, specificity, accuracy, and Youden index as performance metrics to evaluate the proposed method.

Results

This study chose 792 samples from the electronic records of 13,421 patients in a community hospital. Each sample included 28 features (24 blood test features and 4 demographic features). The results of evaluation showed that the proposed method selected 9 important features out of the original 28 features and significantly outperformed baseline methods. Their cumulative contribution was 0.51. The WRHFS method achieved a sensitivity of 82.7% (329/398), specificity of 80.4% (317/394), classification accuracy of 81.5% (645/792), and Youden index of 0.63 using only the top 9 features. We have also presented a chart for visualizing the risk of having ischemic strokes.

Conclusions

This study has proposed, developed, and evaluated a new feature selection method for identifying the most important features for building effective and parsimonious models for stroke risk detection. The findings of this research provide several novel research contributions and practical implications.

Fabrication of an ultrasensitive and selective electrochemical aptasensor to detect carcinoembryonic antigen by using a new nanocomposite

A lable-free electrochemical aptasensor was successfully developed for the sensitive detection of carcinoembryonic antigen as a tumor biomarker. To do this, a ternary nanocomposite of hemin, graphene oxide and multi-walled carbon nanotubes was used. The aptamer can be attached to the surface of a hemin, graphene oxide and multi-walled carbon nanotubes glassy carbon electrode through -NHCO- covalent bonds to form a sensing surface. Through fourier transform infrared spectroscopy and scanning electron microscopy, it was indicated that hemin can be successfully incorporated into hemin, graphene oxide and multi-walled carbon nanotubes. Hemin, which protects graphene nanosheets, also serves as an in-situ probe owing to its well-defined redox properties. Multi-walled carbon nanotubes in the modifier enhance conductivity and facilitate the electron transfer between hemin and the glassy carbon electrode. In this study, carcinoembryonic antigen got specifically bound to the aptamer, and the current changes were used for selective and specific detection of that antigen. The devised aptasensor proved to have excellent performance with a wide linear range of 1.0 × 10^-15 - 1.0 × 10^-8 gmL^-1 and a detection limit of 0.82 fg mL^-1. The inter-day and intra-day values of RSD% were obtained in the range of 0.10-2.91 and 2.21-4.56 respectively. According to the experiments conducted on real samples, it may be claimed that the proposed label-free electrochemical aptasensor is capable enough of determining carcinoembryonic antigen in clinical diagnostics.

Multiplex measurement of twelve tumor markers using a GMR multi-biomarker immunoassay biosensor

Tumor markers play an important role in the early diagnosis and therapeutic effect monitoring of tumors. Combined detection of multiple tumor markers is a realistic way of improving the sensitivity and specificity of cancer diagnosis. To achieve this, we studied and designed a giant magneto resistance (GMR) multi-biomarker immunoassay biosensor that can simultaneously detect twelve kinds of tumor markers by integrating a GMR sensor chip, a microfluidic device, a magnetic nano-beads label, and a double antibody sandwich immunoassay method. As a proof of concept, the proposed immunosensor was utilized to detect 12 tumor markers (AFP, CEA, CYFRA21-1, NSE, SCC, PG I, PG II, CA19-9, total PSA, free PSA, free-β-hCG, Tg) and to screen patients with lung cancer, liver cancer, digestive tract cancer, prostatic cancer, etc. The immunosensor showed excellent sensitivity, accuracy, precision and stability. Designed as a POCT device, the immunosensor also allows for portability, able to perform rapid detection wherever necessary. As a multi-analyte assay, it provides significant advantages over single-analyte tests in terms of cost per test, labor and convenience. The system's ability to simultaneously measure the concentration of multiple markers in serum samples with excellent sensitivity and accuracy allows the immunosensor to be used for early tumor diagnosis.

Ultrasensitive Enzyme-free Biosensor by Coupling Cyclodextrin Functionalized Au Nanoparticles and High-Performance Au-Paper Electrode

Microfluidic paper-based analytical device (μPAD), originally developed for improving healthcare in developing countries, presents a simple yet powerful platform for performing low-cost and portable diagnostic devices. Here, we report an enzyme-free μPAD for the detection of two tumor markers. First, a porous structure of gold nanoparticle (AuNP)-modified paper working electrode (Au-PWE), with a feature of all-round conductivity and plenty of active sites favoring biological ligand attachment, was fabricated as a sensor substrate. Next, cyclodextrin functionalized AuNPs (CD@AuNPs) as dual mimicking enzyme were prepared to load secondary antibodies or peptide. On one sample zone, in the presence of carcinoembryonic antigen (CEA), CD@AuNPs could be introduced into the Au-PWE through a sandwich immunoreaction, boosting the electrochemical signal of o-phenylenediamine (o-PD) via the trigger of a cascade catalysis reaction toward glucose and o-PD, eventually resulting in the sensitive detection of CEA. On another working zone, with the introduction of another target prostate-specific antigen (PSA), peptide cleavage took place, which further led to CD@AuNPs being released from Au-PWE, and then, the variation of electrochemical signals was recorded for the detection of PSA. We demonstrated, using the device, that the detection of CEA and PSA clinically had high sensitivity, wide linear ranges, and low detection limits. We believe that our work provides a promising platform for point-of-care testing, especially in resource-limited regions.

Highly sensitive sensing of hydroquinone and catechol based on β-cyclodextrin-modified carbon dots

In the proposed study, an efficient method for a carbon dot@β-cyclodextrin (C-dot@β-CD)-based fluorescent probe was developed for the analyses of catechol (CC) and hydroquinone (HQ) at trace levels in water samples. The properties of C-dot@β-CD nanocomposites were characterized by Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The sensing behaviors of C-dot@β-CD toward CC and HQ were investigated by fluorescence spectroscopy. Based on the host–guest chemistry between C-dot@β-CD and phenolic compounds, which can quench C-dot@β-CD fluorescence, the prepared C-dot@β-CD nanocomposites could be used for the sensitive and selective detection of CC or HQ across a wide linear range (0.1 to 10 μM) with detection limits of 47.9 and 20.2 nM, respectively. These results showed that the synthesized C-dot@β-CD nanocomposite exhibited strong fluorescence and high degree of water solubility and thus, it is suitable for use as a nanoprobe for detecting CC or HQ in real water samples.

In the proposed study, an efficient method for a carbon dot@β-cyclodextrin (C-dot@β-CD)-based fluorescent probe was developed for the analyses of catechol (CC) and hydroquinone (HQ) at trace levels in water samples.

One-step microwave synthesis of carbon dots for highly sensitive and selective detection of copper ions in aqueous solution

Schematic illustration of the synthesis of CDs and the recognition process for Cu²⁺.

Rotational paper-based electrochemiluminescence immunodevices for sensitive and multiplexed detection of cancer biomarkers

This paper describes a novel rotational paper-based analytical device (RPAD) to implement multi-step electrochemiluminescence (ECL) immunoassays. The integrated paper-based rotational valves can be easily controlled by rotating paper discs manually and this advantage makes it user-friendly to untrained users to carry out the multi-step assays. In addition, the rotational valves are reusable and the response time can be shortened to several seconds, which promotes the rotational paper-based device to have great advantages in multi-step operations. Under the control of rotational valves, multi-step ECL immunoassays were conducted on the rotational device for the multiplexed detection of carcinoembryonic antigen (CEA) and prostate specific antigen (PSA). The rotational device exhibited excellent analytical performance for CEA and PSA, and they could be detected in the linear ranges of 0.1-100 ng mL^-1 and 0.1-50 ng mL^-1 with detection limits down to 0.07 ng mL^-1 and 0.03 ng mL^-1, respectively, which were within the ranges of clinical concentrations. We hope this technique will open a new avenue for the fabrication of paper-based valves and provide potential application in clinical diagnostics.

Cerium Dioxide-Mediated Signal "On-Off" by Resonance Energy Transfer on a Lab-On-Paper Device for Ultrasensitive Detection of Lead Ions

In this report, a 3D microfluidic lab-on-paper device for ultrasensitive detection of lead cation was designed using phoenix tree fruit-shaped CeO₂ nanoparticles (PFCeO₂ NPs) as the catalyst and 50 nm silver NPs (Ag NPs) as the quencher. First, snowflake-like Ag NPs were grown on the paper working electrode through an in situ growth method and used as a matrix for DNAzymes that were specific for lead ions (Pb²⁺). After the addition of Ag NP-labeled substrate strands, the Ag NPs restrained the electrochemiluminescence (ECL) intensity of luminol greatly through the resonance energy transfer from luminol to Ag NPs. However, under the existence of Pb²⁺, the substrate strands were separated, and then PFCeO₂ NP-labeled signal strands were hybridized with the DNAzymes. The ECL signal was improved greatly under the fast catalytic reaction between PFCeO₂ NPs and H₂O₂, which converted the response from signal off to signal on state, resulting in sensitive detection of Pb²⁺. Under the optimal conditions, the ECL signal response exhibited a good linear relationship with the logarithm of lead cation in a wide linear range of 0.05-2000 nM and an ultralow detection limit of 0.016 nM. Meanwhile, a sensor featured with good specificity, acceptable stability, reproducibility, and low cost provides a promising portable, simple, and effective strategy for Pb²⁺ detection.

An ultrasensitive enzyme-free electrochemical immunosensor based on redox cycling amplification using methylene blue

We report a new enzyme-free electrochemical sensor for ultrasensitive measurements of protein biomarkers in plasma and whole blood samples based on a unique electrochemical-chemical-chemical (ECC) redox cycling signal amplification scheme. This scheme uses methylene blue (MB) as a redox indicator which undergoes an endergonic reaction with Ru(NH3)63+ and a highly exergonic reaction with tris(2-carboxyethyl)phosphine (TCEP). This approach offers improved detection sensitivity and sensor stability compared with enzyme-based ECC redox cycling techniques, while involving a simpler sensor modification process and detection protocol. This redox cycling scheme was combined with a robust immunosandwich assay for quantitative measurements of protein biomarkers. For proof of principle, Plasmodium falciparum histidine-rich protein 2 (PfHRP2) was measured in human plasma and whole blood samples, which could be detected down to 10 fg mL-1 and 18 fg mL-1, respectively. Furthermore, this immunosensor exhibits high selectivity, excellent reproducibility and good stability for up to 2 weeks, making it a promising platform for point-of-care testing, especially for detecting extremely low biomarker concentrations in raw biofluids.

Multiplex Immunosensor Arrays for Electrochemical Detection of Cancer Biomarker Proteins

Measuring panels of protein biomarkers offer a new personalized approach to early cancer detection, disease monitoring and patients' response to therapy. Multiplex electrochemical methods are uniquely positioned to provide faster, more sensitive, point of care (POC) devices to detect protein biomarkers for clinical diagnosis. Nanomaterials-based electrochemical methods offer sensitivity needed for early cancer detection. This review discusses recent advances in multiplex electrochemical immunosensors for cancer diagnostics and disease monitoring. Different electrochemical strategies including enzyme-based immunoarrays, nanoparticle-based immunoarrays and electrochemiluminescence methods are discussed. Many of these methods have been integrated into microfluidic systems, but measurement of more than 2-4 protein markers in a small single serum sample is still a challenge. For POC applications, a simple, low cost method is required. Major challenges in multiplexed microfluidic immunoassays are reagent additions and washing steps that require creative engineering solutions. 3-D printed microfluidics and paper-based microfluidic devices are also explored.

Preparation of Au-polydopamine functionalized carbon encapsulated Fe₃O₄ magnetic nanocomposites and their application for ultrasensitive detection of carcino-embryonic antigen

A novel carbon encapsulated Fe3O4 nanoparticles embedded in two-dimensional (2D) porous graphitic carbon nanocomposites (Fe3O4@C@PGC nanocomposites) were synthesized by situ synthesis strategy, which provided a sensor platform owing to a large aspect ratio and porous structure. Polydopamine (PDA) were modified on the surface of Fe3O4@C@PGC nanocomposites through self-polymerization of dopamine, acting as both the reductant and template for one-step synthesis of gold nanoparticles. The prepared Au/PDA/Fe3O4@C@PGC nanocomposites show ferromagnetic features, extremely excellent electron transfer, large specific surface area and excellent dispersing property. These are conducive to the electrochemical signal output and the immobilization of antibody. In this work, a highly label-free sensitive magnetic immunosensor was developed based on Au/PDA/Fe3O4@C@PGC nanocomposites for the detection of carcino-embryonic antigen (CEA). The magnetic glassy carbon electrode was used to fix the Au/PDA/Fe3O4@C@PGC nanocomposites with the help of magnetic force. Under the optimal conditions, the immunosensor exhibited a wide linear range (0.001 ng/mL-20.0 ng/mL), a low detection limit (0.33 pg/mL), good reproducibility, selectivity and acceptable stability. The proposed sensing strategy may provide a potential application in the detection of other cancer biomarkers.

An electrochemical immunosensor for simultaneous point-of-care cancer markers based on the host–guest inclusion of β-cyclodextrin–graphene oxide

An electrochemical immunosensor was developed using GO–AuNPs as substrates, Cu₂O–GO–CD and GO–CD–Fc as probes, which exhibited excellent electrochemical performances.

Efficient electrochemiluminescence quenching of carbon-coated petalous CdS nanoparticles for an ultrasensitive tumor marker assay through coreactant consumption by G-quadruplex-hemin decorated Au nanorods

A novel competitive electrochemiluminescence aptasensor was designed for the detection of carcinoembryonic antigen using carbon-coated petalous CdS nanopaticles as an ECL emitter and DNAzyme/Au nanorods–complementary DNA as a quenching probe.

An enhanced photoelectrochemical platform: graphite-like carbon nitride nanosheet-functionalized ZnO nanotubes

Large-scale two-dimensional graphite-like carbon nitride nanosheets with obvious upconversion properties were prepared by a liquid exfoliation route and used to functionalize ZnO nanotubes to construct a photoelectrochemical platform.