Improved ELISA for tumor marker detection using electro-readout-mode based on label triggered degradation of methylene blue

Surface-enhanced Raman sensor with molecularly imprinted nanoparticles as highly sensitive recognition material for cancer marker amino acids

Surface-enhanced Raman scattering (SERS) is a powerful technique primarily due to its high sensitivity and signal-enhancing properties, which enable the identification of unique vibrational fingerprints. These fingerprints can be used for the diagnosis and monitoring of diseases such as cancer. It is crucial to selectively identify cancer biomarkers for early diagnosis. A correlation has been established between the reduction in the concentration of specific amino acids and the stage of the disease, particularly tryptophan (TPP) and tyrosine (TRS) in individuals diagnosed with prostate cancer. In this work, we present a strategy to analyze TPP and TRS amino acids using molecularly imprinted polymer nanoparticles (nanoMIPs), which selectively detect target molecules in a SERS sensor. NanoMIPs are synthesized using the solid-phase molecular imprinting method with TPP and TRS as templates. These are then immobilized on a SERS substrate with gold nanoparticles to measure samples prepared from tryptophan and tyrosine in phosphate-buffered saline. The detection and quantification limits of the designed sensor are 7.13 μM and 23.75 μM for TPP, and 22.11 μM and 73.72 μM for TRS, respectively. Our study lays the groundwork for future investigations utilizing nanoMIPs in SERS assessments of TPP and TRS as potential biomarkers for prostate cancer detection.

Magnetic microspheres enhanced peanut structure cascaded lasso shaped fiber laser biosensor for cancer marker-CEACAM5 detection in serum

The detection of trace cancer markers in body fluids such as blood/serum is crucial for cancer diseases screening and treatment, which requires high sensitivity and specificity of biosensors. In this study, a peanut structure cascaded lasso (PSCL) shaped fiber sensing probe based on fiber laser demodulation method was proposed to specifically detect the carcinoembryonic antigen related cell adhesion molecules 5 (CEACAM5) protein in serum. Thanks for the narrow linewidth and high signal-to-noise ratio (SNR) of the laser spectrum, it is easier to distinguish small spectral changes than interference spectrum. Adding the antibody modified magnetic microspheres (MMS) to form the sandwich structure of "antibody-antigen-antibody-MMS", and amplified the response caused by biomolecular binding. The limit of detection (LOD) for CEACAM5 in buffer could reach 0.11 ng/mL. Considering the common threshold of 5 ng/mL for CEA during medical screening and the cut off limit of 2.5 ng/mL for some kits, the LOD of proposed biosensor meets the actual needs. Human serum samples from a hospital were used to validate the real sensing capability of proposed biosensor. The deviation between the measured value in various serum samples and the clinical value ranged from 1.9 to 9.8 %. This sensing scheme holds great potential to serve as a point of care testing (POCT) device and extend to more biosensing applications.

Quantification of Glycated Hemoglobin in Total Hemoglobin by a Simultaneous Dual-Signal Acquisition Approach

The glycated hemoglobin (HbA1c) level, which is defined as the ratio of HbA1c to total hemoglobin (tHb, including glycated and unglycated hemoglobin), is considered one of the preferred indicators for diabetes monitoring. Generally, assessment of the HbA1c level requires separate determination of tHb and HbA1c concentrations after a complex separation step. This undoubtedly increases the cost of the assay, and the loss or degradation of HbA1c during the separation process results in a decrease in the accuracy of the assay. Therefore, this study explored a dual-signal acquisition method for the one-step simultaneous evaluation of tHb and HbA1c. Quantification of tHb: graphene adsorbed carbon quantum dots and methylene blue were utilized as the substrate material and linked to the antibody. tHb was captured on the substrate by the antibody. The unique heme group on tHb catalyzed the production of •OH from H2O2 to degrade methylene blue on the substrate, and a quantitative relationship between the tHb concentration and the methylene blue oxidation current signal was constructed. Quantification of HbA1c: complex labels with HbA1c recognition were made of ZIF-8-ferrocene-gold nanoparticles-mercaptophenylboronic acid. The specific recognition of the boronic acid bond with the unique cis-diol structure of HbA1c establishes a quantitative relationship between the oxidation current of the label-loaded ferrocene and the concentration of HbA1c. Thus, the HbA1c level can be assessed with only one signal readout. The sensor exhibited extensive detection ranges (0.200-600 ng/mL for tHb and 0.100-300 ng/mL for HbA1c) and low detection limits (4.00 × 10-3 ng/mL for tHb and 1.03 × 10-2 ng/mL for HbA1c).

Exclusive Core-Janus Satellite Assembly Based on Au-Ag Janus Self-Aligned Distributions with Abundant Hotspots for Ultrasensitive Detection of CA19-9

The development of surface-enhanced Raman scattering (SERS) probes with high sensitivity and stability is imminent to improve the accuracy of cancer diagnosis. Here, an exclusive core-Janus satellite (CJS) assembly was constructed by a hierarchical assembly strategy in which the Au-Ag Janus satellite is vertically self-aligned on the core surface. In the process, a silica shell template was ingeniously employed to asymmetrically mask the presatellites for the in situ formation of the Janus structure, and a series of Janus satellites with different morphologies were developed by regulating the encapsulated area of the presatellites. The ordered-oriented arrangement of Au-Ag Janus and unique heterojunction morphology permit CJS assemblies, featuring two types of plasmonic nanogaps, including intrananocrevices for individual Janus and internanogaps between neighboring Janus, thereby multiplying the "hotspots" compared to conventional core-monotonous satellites, which contributes to superior SERS activity. As anticipated, the enhancement factor of CJS assemblies was as high as 3.8 × 108. Moreover, it is intriguing that the directional distribution and head physically immobilized by Janus provided uniform and stable SERS signals. The SERS probe based on the CJS assembly for the detection of carbohydrate antigen 19-9 resulted in an ultrahigh sensitivity with a limit of detection of 3.7 × 10-5 IU·mL-1, which is nearly 10 times lower than other SERS probes, and a wide detection range of 3 × 10-5 to 1 × 104 IU·mL-1. The CJS assembly with excellent SERS performance is promising to advance further development of the early diagnosis of pancreatic cancer.

A colorimetric aptasensor for CA125 determination based on dual catalytic performance of CeO2 nanozyme confined in macroporous silica foam

A portable colorimetric aptasensor was constructed based on the dual catalytic performance of CeO2 nanozyme to determine carbohydrate antigen 125 (CA125). Firstly, CeO2 nanozyme was synthesized by calcination and ultrasonically dispersed in a macroporous silica foam (MSF) to form CeO2@MSF. Then the aptamer of CA125 (apt) and complementary DNA (c-DNA) were successively assembled on the CeO2@MSF to construct a CeO2@MSF/apt/c-DNA colorimetric aptasensor, which exhibited excellent oxidase-mimic performance and phosphatase-mimic activity simultaneously. In the presence of CA125, the apt specifically binds to target CA125, and the single-strand c-DNA leaves the CeO2@MSF/apt surface, which is catalytically hydrolyzed by exonuclease I. The produced phosphate ions inhibit the phosphatase-mimic activity of CeO2 nanozyme. Thus, the absorbance at 652 nm of 3,3',5,5'-tetramethylbenzidine solution containing ascorbic acid-2-phosphate increases with the concentration of CA125. The response is linearly related to the logarithm of CA125 concentration from 1.0 to 10.0 U/mL under optimal experimental conditions. Based on this, the constructed colorimetric aptasensor has a high sensitivity, good selectivity, and high accuracy for CA125 determination in real human serum sample.

Colorimetric and photothermal immunosensor for sensitive detection of cancer biomarkers based on enzyme-mediated growth of gold nanostars on polydopamine

BACKGROUND

Detecting cancer biomarker levels in body fluids is essential for medical diagnosis. Enzyme-linked immunosorbent assay (ELISA) has been broadly used to detect cancer biomarkers. However, colorimetric ELISA based solely on nanoparticles (NPs) are susceptible to environmental influences, which often results in the detection inaccuracy, being limited in clinical applications. In this regard, the dual-mode approach would add signal diversity to the detection, making the results more reliable.

RESULTS

We present colorimetric and photothermal immunosensor that enables direct reading of the color and temperature of the solution. A core-satellite nanoprobe constructed by polydopamine (PDA) as the core and gold seeds as satellites is rationally designed as the signal reporter. When ascorbic acid is present in the solution, PDA can cooperate with ascorbic acid to reduce chloroauric acid and mediate the growth of gold seeds on the PDA surface, inducing a redshift of the localized surface plasmon resonance peak of the nanosensor and the change in photothermal conversion efficiency. The method is further combined with the sandwiched immunoassay to construct an alkaline phosphatase based colorimetric and photothermal ELISA for the highly sensitive and accurate evaluation and detection of prostate-specific antigen (PSA). The linear range was from 0.05 to 100 ng mL-1 with a detection limit of 6.71 pg mL-1 for the colorimetric detection, while the linear range was from 0.5 to 90 ng mL-1 with a detection limit of 0.13 ng mL-1 in the photothermal analysis. The accurate detection of PSA levels in serum samples was well demonstrated with the dual-mode approach.

SIGNIFICANCE

The presented immunoassay allows straightforward, sensitive, and selective readout by color and temperature without advanced instrumentation. Particularly, the LOD was much lower than the threshold in clinical trials for PSA. Therefore, this method has a great prospect in the early diagnosis of cancer biomarkers based on a dual-mode multifunctional platform.

Anti-Fouling Strategies of Electrochemical Sensors for Tumor Markers

The early detection and prognosis of cancers require sensitive and accurate detection methods; with developments in medicine, electrochemical biosensors have been developed that can meet these clinical needs. However, the composition of biological samples represented by serum is complex; when substances undergo non-specific adsorption to an electrode and cause fouling, the sensitivity and accuracy of the electrochemical sensor are affected. In order to reduce the effects of fouling on electrochemical sensors, a variety of anti-fouling materials and methods have been developed, and enormous progress has been made over the past few decades. Herein, the recent advances in anti-fouling materials and strategies for using electrochemical sensors for tumor markers are reviewed; we focus on new anti-fouling methods that separate the immunorecognition and signal readout platforms.

Dumbbell-like upconversion nanoparticles synthesized by controlled epitaxial growth for light-heat-color tri-modal sensing of carcinoembryonic antigen

Accurate quantitative analysis of tumor markers in a wide linear range has important practical significance towards complex clinical samples in cancer identification and monitoring of tumor development stages, but remains challenging. Herein, three-layer dumbbell-like upconversion nanoparticles NaErF₄:Tm@NaYF₄@NaNdF₄ (labeled as UCNPs) combined with G-quadruplex (G₄) DNAzyme are reported for tri-modal sensing of carcinoembryonic antigen (CEA) in a wide range using upconversion luminescence (UCL), photothermal and catalysis signal readouts. Initially, dumbbell-like UCNPs were controlled synthesized by a three-dimensional epitaxial growth strategy through tuning the concentration of Nd precursors. After surface functionalization, G₄zyme-UCNPs-cDNA/Apt-MB was subsequently fabricated by biotin-streptavidin interaction and DNA hybridization. Quantitative detection of CEA was achieved by competitive interaction and magnetic separation, and the intensities of tri-modal signals (light, heat and catalysis-based chrominance) of dissociative probes are linearly related to the concentration of CEA. The results showed that the tri-modal sensing method exhibited a wide linear range (0.005-2000 ng/mL) and low limit of detection (LOD) across three models: the luminescence model (0.005-50 ng/mL, LOD = 0.910 pg/mL), the catalysis model (10-1000 ng/mL, LOD = 0.387 ng/mL), and the temperature model (50-2000 ng/mL, LOD = 1.114 ng/mL). These findings suggest that the tri-modal sensing platform is suitable for use in the analysis of a wide range of complex and diverse clinical samples.

Ratiometric fluorescent Si-FITC nanoprobe for immunoassay of SARS-CoV-2 nucleocapsid protein

Coronavirus disease 2019 (COVID-19) highlights the importance of rapid and reliable diagnostic assays for the management of virus transmission. Here, we developed a one-pot hydrothermal method to prepare Si-FITC nanoparticles (NPs) for the fluorescent immunoassay of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) nucleocapsid protein (N protein). The synthesis of Si-FITC NPs did not need post-modification, which addressed the issue of quantum yield reduction during the coupling reaction. Si-FITC NPs showed two distinct peaks, Si fluorescence at λ em = 385 nm and FITC fluorescence at λ em = 490 nm. In the presence of KMnO4, Si fluorescence was decreased and FITC fluorescence was enhanced. Briefly, in the presence of N protein, catalase (CAT)-linked secondary antibody/reporter antibody/N protein/capture antibody immunocomplexes were formed on microplates. Subsequently, hydrogen peroxide (H2O2) and Si-FITC NPs/KMnO4 were injected into the microplate together. The decomposition of H2O2 by CAT resulted in remaining of KMnO4, which changed the fluorescence intensity ratio of Si-FITC NPs. The fluorescence intensity ratio correlated significantly with the N protein concentration ranging from 0.02 to 50.00 ng/mL, and the detection limit was 0.003 ng/mL, which was more sensitive than the commercial ELISA kit with a detection limit of 0.057 ng/mL. The N protein concentration can be accurately determined in human serum. Furthermore, the COVID-19 and non-COVID-19 patients were distinguishable by this method. Therefore, the ratiometric fluorescent immunoassay can be used for SARS-CoV-2 infection diagnosis with a high sensitivity and selectivity.

Electronic Supplementary Material

Supplementary material (characterization of Si-FITC NPs (FTIR, HRXPS); stability investigation of Si-FITC NPs (photostability, pH stability, anti-interference ability); stability investigation of free FITC (pH value, KMnO4); quenching mechanism of KMnO4 (UV-vis absorption spectra, fluorescence lifetime decay curves); reaction condition optimization of biotin-CAT with H2O2 (pH value, temperature, time); detection of N protein using commercial ELISA Kit; selectivity investigation of assays for SARS-CoV-2 N protein detection; determination results of SARS-CoV-2 N protein in human serum) is available in the online version of this article at 10.1007/s12274-022-5005-z.

A chemiluminescence aptasensor for sensitive detection of alpha-fetoprotein based on hemin@ZIF-67

In this work, hemin@ZIF-67 composites were prepared and were used to construct a chemiluminescence (CL) aptasensor for alpha-fetoprotein (AFP) detection. Hemin is a catalytic porphyrin with two carboxylate groups that can covalently bond to metal ions. A hemin/ZIF-67 composite was prepared via covalent bonding between the carboxyl groups of hemin and the cobalt ion of ZIF-67, and these materials were characterized by scanning electron microscopy (SEM), infrared spectroscopy (IR), and X-ray diffraction (XRD). Hemin@ZIF-67 was used as the peroxidase material, and the aptamer of alpha-fetoprotein was modified on its surface by electrostatic adsorption. Then a simple CL aptasensor was constructed based on the CL system of luminol-H₂O₂-NaOH. Under the optimal conditions, the CL intensity value was linearly proportional to the concentration of AFP in the range of 4 × 10^-10 to 200 × 10^-10 mg/mL. The detection limit was 1.3 × 10^-10 mg/mL. Thus the aptasensor enables highly sensitive and selective detection of AFP.

Cancer glycomics offers potential biomarkers and therapeutic targets in the framework of 3P medicine

Glycosylation is one of the most important post-translational modifications (PTMs) in a protein, and is the most abundant and diverse biopolymer in nature. Glycans are involved in multiple biological processes of cancer initiation and progression, including cell-cell interactions, cell-extracellular matrix interactions, tumor invasion and metastasis, tumor angiogenesis, and immune regulation. As an important biomarker, tumor-associated glycosylation changes have been extensively studied. This article reviews recent advances in glycosylation-based biomarker research, which is useful for cancer diagnosis and prognostic assessment. Truncated O-glycans, sialylation, fucosylation, and complex branched structures have been found to be the most common structural patterns in malignant tumors. In recent years, immunochemical methods, lectin recognition-based methods, mass spectrometry (MS)-related methods, and fluorescence imaging-based in situ methods have greatly promoted the discovery and application potentials of glycomic and glycoprotein biomarkers in various cancers. In particular, MS-based proteomics has significantly facilitated the comprehensive research of extracellular glycoproteins, increasing our understanding of their critical roles in regulating cellular activities. Predictive, preventive and personalized medicine (PPPM; 3P medicine) is an effective approach of early prediction, prevention and personalized treatment for different patients, and it is known as the new direction of medical development in the 21st century and represents the ultimate goal and highest stage of medical development. Glycosylation has been revealed to have new diagnostic, prognostic, and even therapeutic potentials. The purpose of glycosylation analysis and utilization of biology is to make a fundamental change in health care and medical practice, so as to lead medical research and practice into a new era of 3P medicine.

A Label-Free Electrochemical Immunosensor for CEA Detection on a Novel Signal Amplification Platform of Cu2S/Pd/CuO Nanocomposites

Carcinoembryonic antigen (CEA) is regarded as one of the crucial tumor markers for colorectal cancer. In this study, we developed the snowflake Cu₂S/Pd/CuO nanocomposite to construct an original label-free electrochemical immunosensor for the ultrasensitive detection of CEA levels. The nanocomposite of cuprous sulfide (Cu₂S) with Pd nanoparticles (Pd NPs) was synthesized through an in situ formation of Pd NPs on the Cu₂S. Cuprous sulfide (Cu₂S) and CuO can not only be used as a carrier to increase the reaction area but also catalyze the substrate to generate current signal. Palladium nanoparticles (Pd NPs) have excellent catalytic properties and good biocompatibility, as well as the ability of excellent electron transfer. The immunosensor was designed using 5 mmol/L H₂O₂ as the active substrate by optimizing the conditions with a detection range from 100 fg/ml to 100 ng/ml and a minimum detection limit of 33.11 fg/ml. The human serum was detected by electrochemical immunoassay, and the results were consistent with those of the commercial electrochemical immunosensor. Therefore, the electrochemical immunosensor can be used for the detection of human serum samples and have potential value for clinical application.

A Systematic Study and Potential Limitations of Proton-ELISA Platform for α-Synuclein Antigen Detection

To evaluate point-of-care testing (POCT) for the potential early detection of biomarkers of Parkinson’s disease, a systematic investigation of portable and low-cost platforms is performed based on the Proton-enzyme-linked immunosorbent assay (Proton-ELISA) methodology. The detection of the α-synuclein antigen was first presented by biotin-relative linkers, and glucose substrate solution was first performed with a systematic experimental design to optimize the sensing results. All materials in this study are commercially available. Three different experiments with the partitional check were performed to investigate the Proton-ELISA platform, including proton catalyzed efficiency, blocking efficiency, and full Proton-ELISA procedure. The response time was selected as 15 min by the time-dependent curves of a full reaction. The limit of detection of conventional ELISA kits is 0.169 ng/mL, which is much lower than the Proton-ELISA results. The final response of the full Proton-ELISA procedure to pH changes was approximately 0.60 and 0.12 for α-synuclein antigen concentrations of 100 ng/mL and 4 ng/mL, respectively. With the partitional check, pH changes of pure glucose substrate and conjugated oxidase and interference of the nonspecific binding are 1.7 and 0.04, respectively. The lower pH changes far from the partitional check results can be concluded for the properties of glucose oxidase conjugation, including the isoelectric point and binding affinity modification by the testing environment. This preliminary guideline can be used as a lesson learnt to speed up following studies of the evaluation and optimization of other antigen detection. Therefore, Proton-ELISA can be suggested for some special applications with the help of custom-designed conjugation in the environment with less degradation or interference and a proper detection concentration range.

Responsive-released strategy based on lead ions-dependent DNAzyme functionalized UIO-66-NH2 for tumor marker

Signal labeling on electrode interface is an important step during the construction of immunosensor and most signal substances are directly affixed on the immunoprobe or substrate so that some problems such as flimsy labeling method and interference of insulating proteins on electrode surface have been existed to affect their readout. In order to solve above problems in electrochemical immunoassay, a lead ions-decodable autocephalous signal integrator based on UIO-66-NH₂ was proposed for the detection of prostate specific antigen (PSA). Briefly, a lead ions-dependent DNAzyme functionalized UIO-66-NH₂, in which methylene blue was encapsulated, was independently dispersed in solution phase to be closely associated with the lead sulfide labeled sandwich bioconjugates, and internal methylene blue molecules can be sustained released once a cationic exchange reaction was occurred between lead sulfide label and adscititious silver ions. Based on this designing, immunoassay for PSA was effectively connected with the dynamic behavior of methylene blue molecules through the cleavage of DNAzyme on MOFs surface and performed a wide linear range from 1 pg mL^-1 to 10 ng mL^-1 and a satisfactory detection limit with 0.34 pg mL^-1. The proposed strategy was expected to offer more valuable information for the application of MOFs in early and accurate cancer 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.

New Tool for Rapid and Accurate Detection of Interleukin-2 and Soluble Interleukin-2 Receptor α in Cancer Diagnosis Using a Bioresponsive Microgel and Multivalent Protein Binding

Interleukin-2 (IL-2) and its α receptor in soluble form (sIL-2Rα) are considered biomarkers for cancers and immune-related diseases. Enzyme-linked immunosorbent assay is the most common method used to evaluate biomarkers in clinical practice; it is precise but time-consuming and involves complicated procedures. Here, we have developed a rapid yet accurate modality for cancer diagnosis that enables on-site evaluation of cancer markers, that is, IL-2 and sIL-2Rα, without complicated pretreatment of cancer patient-derived blood samples. Surface plasmon resonance and bioresponsive microgels conjugated with IL-2 receptors, that is, IL-2Rβ and IL-2Rγ, were utilized to measure IL-2 and sIL-2Rα levels via multivalent protein binding (MPB) between the ligands and their receptors. Our results showed that this novel method enables us to perform cancer diagnosis with a 1000-fold dilution of serum in 10 min. The advantage of MPB-based cancer diagnosis originates from its great selectivity for a target molecule and tolerance to a myriad of nonspecific substances in serum, which allows on-site clinical evaluation. Importantly, our finding implies that MPB-based cancer diagnosis provides a new paradigm not only for improving cancer treatment but also for evaluating a target molecule in unpurified and complex solutions such as blood.

A Microfluidic Chip-Based MRS Immunosensor for Biomarker Detection via Enzyme-Mediated Nanoparticle Assembly

Conventional immunoassay methods have their common defects, such as tedious processing steps and inadequate sensitivity, in detecting whole blood. To overcome the above problems, we report a microfluidic chip-based magnetic relaxation switching (MRS) immunosensor via enzyme-mediated nanoparticles to simplify operation and amplify the signal in detecting whole blood samples. In the silver mirror reaction with catalase (CAT) as the catalyst, H2O2 can effectively control the production of Ag NPs. The amount of Ag NPs formed further affects the degree of aggregation of magnetic nanoparticles (MNPS), which gives rise to the changes of transverse relaxation time (T2). Both sample addition and reagent reaction are carried out in the microfluidic chip, thereby saving time and reagent consumption. We also successfully apply the sensor to detect alpha-fetoprotein (AFP) in real samples with a satisfied limit of detection (LOD = 0.56 ng/ml), which is superior to the conventional ELISA.

Fenton reaction-mediated dual-attenuation of signal for ultrasensitive amperometric immunoassay

In order to alter the complexion of immunoprobe with large impedance as negative factor in sensitivity of amperometric immunosensor, a strategy of Fenton reaction-mediated dual-attenuation of signal was proposed. Herein, metal-polydopamine-Fe³⁺ composite with the ability of Fenton reaction was initially prepared as immunoprobe for an ultrasensitive immunoassay. The polymerization of dopamine occurred on the surface of ZIF-67 to gain the metal-polydopamine shell, which possessed rich functional groups, negative charge and high specific surface. Then the prepared functional shell was further used to absorb Fe³⁺ and immobilize labeling antibody as immunoprobe, which was used to construct a sandwich type immunosensor. With addition of H₂O₂ and aniline, Fenton reaction was triggered to produce hydroxyl radicals, which can not only decrease the current value by degrading methylene blue molecules, but also further initiate aniline to polymerize into non-conductive polyaniline for successive abatement of signal intensity. Therefore, the dual-attenuation of signal model rendered the immunoprobe into a favorable factor and synchronously enhance sensitivity. Expectedly, the detection performance with a linear range from 1.0 × 10^-4-100 ng mL^-1 and ultralow detection limit of 9.07 × 10^-5 ng mL^-1 toward neuron-specific enolase was obtained under optimal conditions. This work offered a novel tactic for enhancing sensitivity of immunosensor through the preparation of functional immunoprobe and its rational utilization as signal enhancer.

Recent advances in nanoscale materials for antibody-based cancer theranostics

The quest for advanced management tools or options of various cancers has been on the rise to efficiently reduce their risks of mortality without the demerits of conventional treatments (e.g., undesirable side effects of the medications on non-target tissues, non-targeted distribution, slow clearance of the administered drugs, and the development of drug resistance over the duration of therapy). In this context, nanomaterials-antibody conjugates can offer numerous advantages in the development of cancer theranostics over conventional delivery systems (e.g., highly specific and enhanced biodistribution of the drug in targeted tissues, prolonged systemic circulation, low toxicity, and minimally invasive molecular imaging). This review comprehensively discusses and evaluates recent advances in the application of nanomaterial-antibody bioconjugates for cancer theranostics for the further advancement in the control of diverse cancerous diseases. Further, discussion is expanded to cover the various challenges and limitations associated with the design and development of nanomaterial-antibody conjugates applicable towards better management of cancer.

Ultrasensitive microfluidic electrochemical immunosensor based on electrodeposited nanoporous gold for SOX-2 determination

An ultrasensitive and portable microfluidic electrochemical immunosensor for SOX-2 cancer biomarker determination was developed. The selectivity and sensitivity of the sensor were improved by modifying the microfluidic channel. This was accomplished through a physical-chemical treatment to produce a hydrophilic surface, with an increased surface to volume/ratio, where the anti-SOX-2 antibodies can be covalently immobilized. A sputtered gold electrode was used as detector and its surface was activated by using a dynamic hydrogen bubble template method. As a result, a gold nanoporous structure (NPAu) with outstanding properties, like high specific surface area, large pore volume, uniform nanostructure, good conductivity, and excellent electrochemical activity was obtained. SOX-2 present in the sample was bound to the anti-SOX-2 immobilized in the microfluidic channel, and then was labeled with a second antibody marked with horseradish peroxidase (HRP-anti-SOX-2) like a sandwich immunoassay. Finally, an H₂O₂ + catechol solution was added, and the enzymatic product (quinone) was reduced on the NPAu electrode at +0.1 V (vs. Ag). The current obtained was directly proportional to the SOX-2 concentration in the sample. The detection limit achieved was 30 pg mL^-1, and the coefficient of variation was less than 4.75%. Therefore, the microfluidic electrochemical immunosensor is a suitable clinical device for in situ SOX-2 determination in real samples.

Functional nanomaterials based immunological detection of aflatoxin B1: a review

Aflatoxin B1 (AFB1) is highly carcinogenic, mutagenic and teratogenic. Accordingly, sensitive, rapid and cost-effective techniques for detection of AFB1 is in urgent demand for food safety and the health of consumers. In this review, we report the current state of immunoassay formats and development, mainly based on nanomaterials for determination of AFB1. Following an introduction of the field, the microplate-, membrane- and microelectrode-based immunoassays are described. The relevant mechanisms, sensitivities, superiorities and deficiencies of each format are discussed. Finally, perspectives on the future development of nanomaterials-based immunoassays for AFB1 are provided.

Purification and separation of ultra-small metal nanoclusters

Metal nanoclusters (NCs) are ultra-small nanoparticles intermediate in size between small molecule complexes and nanoparticles. NCs with tunable surface functionality feature unique physical and chemical properties, however these properties are frequently compromised by the presence of undesired components such as excess ligands or mixtures of NCs. In a typical synthesis process, different NCs can be formed with varying numbers of metal atoms and/or ligands, and even NCs with the same number of metal atoms and ligands can have different spatial structures. The separation of pure NCs is important because different species have distinct optical and catalytic behavior. However, NCs can be difficult to purify or separate for a range of reasons. In this review, we discuss established and emerging approaches for NC purification/separation, with a focus on choosing the appropriate method depending on NC and application.

The simultaneous detection of the squamous cell carcinoma antigen and cancer antigen 125 in the cervical cancer serum using nano-Ag polydopamine nanospheres in an SERS-based lateral flow immunoassay

The accurate analysis of tumor related biomarkers is extremely critical in the diagnosis of the early stage cervical cancer. Herein, we designed a novel and inexpensive surface-enhanced Raman scattering-based lateral flow assay (SERS-based LFA) strip with a single test line, which was applied for the rapid and sensitive quantitative simultaneous analysis of SCCA and CA125 in serum samples from patients with cervical cancer. In the presence of target antigens, the monoclonal antibody-coupled and Raman reporter-labeled nano-Ag polydopamine nanospheres (PDA@Ag-NPs) aggregated on the test line modified by the polyclonal antibody to form a double-antibody sandwich structure. The finite difference time domain simulation demonstrated that large number of “hot spots” was generated among the nanogaps of aggregated PDA@AgNPs, which resulted in a huge enhancement of the signal of the Raman reporters. Accordingly, the limit of detection was determined to be 7.156 pg mL⁻¹ for SCCA and 7.182 pg mL⁻¹ for CA125 in phosphate buffer and 8.093 pg mL⁻¹ for SCCA and 7.370 pg mL⁻¹ for CA125 in human serum, revealing high sensitivity of this SERS-based LFA strip. Significantly, the detection of SCCA and CA125 using the SERS-based LFA was observed to have high specificity and reproducibility, and the whole detection was completed within 20 min. Furthermore, the SERS-based LFA and enzyme-linked immunosorbent assay were also employed in serum samples obtained from patients with cervical cancer, cervical intraepithelial neoplasia and healthy subjects, and perfect agreement existed between both the methods. Thus, clinically, the developed SERS-based LFA strip has strong potential for the simultaneous detection of multiple cancer biomarkers in serum.

Based on SERS-based lateral flow immunoassay, nano-Ag polydopamine nanospheres was used for detecting squamous cell carcinoma antigen and cancer antigen 125 simultaneously in cervical cancer serum.

Design and fabrication of a microfluidic chip to detect tumor markers

A microfluidic chip based on capillary infiltration was designed to detect tumor markers. Serum samples flowed along a microchannel that used capillary force to drive sample injection, biochemical reactions and waste liquid collection. This permitted us to realize rapid qualitative detection of tumor markers and other biological molecules. The chip integrated a number of microfluidic functions including blood plasma separation, microvalve operation, and antibody immobilization. Using antigen–antibody reaction principles, the chip provided highly selective and sensitive detection of markers. Combining a microfluidic chip with immunoassays not only improved the antigen–antibody reaction speed, but also reduced the consumption of samples and reagents. The experimental results showed that the chip can achieve separation of trace whole blood, control of sample flow rate, and detection of alpha fetoprotein, thus providing preliminary verification of its feasibility and potential for clinical use. In summary, in this paper a cheap, mass-produced, and portable microfluidic chip for cancer detection, which has good prospects for practical use during disease diagnosis and screening is reported.

A microfluidic chip for detecting tumor markers integrated functions including blood plasma separation, microvalve operation, and antibody immobilization.