Bioresponsive Release System for Visual Fluorescence Detection of Carcinoembryonic Antigen from Mesoporous Silica Nanocontainers Mediated Optical Color on Quantum Dot-Enzyme-Impregnated Paper

Enhanced fluorescent sensing probe via PbS quantum dots functionalized with gelatin for sensitive determination of toxic bentazon in water samples

Fluorescent chemical sensors to detect materials, by increasing fluorescence emission and absorption or by shutting down, because they are nondestructive, the ability to show decomposed concentrations, fast response, high accuracy have been considered and used. In this research, a chemical sensor was synthesized PbS functionalized with gelatin quantum dots for the determination of toxic bentazon (BTZN) one of the most problematic pesticides polluting in water samples, and extremely harmful to humans and animals even at low concentrations. The calibration curve was linear in the range of (0.05 to 200.0 ng mL^-1). The current response was linearly proportional to the BTZN concentration with a R²∼ 0.999. The standard deviation of less than (3%), and detection limits (3S/m) of the method (0.5 ng mL^-1, in time 50 s, 325 nm) were obtained for sensor level response PbS Quantum Dot-Gelatin nanocomposites sensor with (99%) which is below the U.S. Health Advisory level. The observed outcomes confirmed the suitability recovery and a very low detection limit for measuring the BTZN. The method fluorometric introduced to measure BTZN in water samples was used and can be used for in different intricate matrices, the chemical PbS Quantum Dot-Gelatin nanocomposites sensor made it possible as an excellent sensor with good reproducibility.

Ultrasensitive and turn-on homogeneous Hg2+ sensing based on a target-triggered isothermal cycling reaction and dsDNA-templated copper nanoparticles

In this work, an ultrasensitive and turn-on sensor for homogeneous Hg2+ detection has been constructed based on a target-triggered isothermal cycling reaction and rapid label-free signal output with dsDNA-templated copper nanoparticles (CuNPs). As the key component of the sensor, a hairpin DNA without any labels was designed to contain different functional sequence segments and to resist digestion by exonuclease due to the protruding 3'-terminus. In the presence of Hg2+, the formation of a T-Hg2+-T structure turned the protruding 3'-terminus of the hairpin DNA to a blunt end that could be efficiently digested by Exo III, accompanied by Hg2+ release, followed by another digestion cycle. Hence, the Hg2+-triggered isothermal cycling reaction accumulated numerous dsDNA templates that facilitated fluorescent CuNP generation and finally output an amplified signal used to identify the target. This protocol is capable of Hg2+ sensing in a concentration range of 5 orders of magnitude with a detection limit down to 3.9 pM. The as-constructed sensor also revealed high selectivity, as well as satisfactory results in recovery experiments of Hg2+ detection in real water samples.

Investigation of the association complex formed between dapoxetine and erythrosine-B for facile dapoxetine assay in pharmaceutical formulation using resonance Rayleigh scattering and spectrofluorimetric techniques

Premature ejaculation is a male sexual problem that is marked by rapid ejaculation and quick attainment of orgasm. Dapoxetine belongs to the antidepressant category and modulates its action by preventing the reuptake of serotonin by neurons. Dapoxetine is marketed as an off-label therapy for premature ejaculation. Here, two facile, sensitive, and green compatible approaches were established for dapoxetine assay. The approaches chemically rely on association complex formed between erythrosine-B and dapoxetine in an acidic buffered medium. The quenching effect of the formed complex on the native erythrosine fluorescence at emission 553.5 nm is simply the main idea of spectrofluorimetric assay, while resonance Rayleigh scattering methodology uses augmentation of resonance Rayleigh scattering spectrum at 345 nm by the added dapoxetine. The current approaches exhibit linearity between response and dapoxetine concentration over 0.2-2.5 μg/ml and 0.3-3.0 μg/ml for spectrofluorimetric and resonance Rayleigh scattering (RRS) methods, respectively. All variables affecting methods and complex formation were studied and precisely optimized. The criteria of validation were performed by the directives provided by International Conference on Harmonization's (ICH) Guidelines and limits of detection were 0.06 and 0.05 μg/ml for spectrofluorimetric and RRS techniques, respectively. Finally, the approaches were applied with acceptable results for pharmaceutical formulation analysis.

Ultrasensitive fluorescence immunosensor based on mesoporous silica and magnetic nanoparticles: Capture and release strategy

Herein we designed a novel, highly sensitive, simple and amplified fluorescence immunosensing strategy for hepatitis B virus surface antigen (HBV surface antigen) (HBsAg) as a model based on the construction of a sandwich type probe. The operation mechanism of this immunosensing strategy is implemented by capturing and then stimulation-based-releasing of entrapped dye in the fluorescent capsules. The proposed probe is made by the Fe₃O₄ magnetic nanoparticle (Fe₃O₄ MNP) as a probe collector site and the Rhodamine B loaded-mesoporous silica nanoparticle (MSN-Rh.B) as a fluorescent mesoporous capsule and signal amplifier site. Such a methodology is benefited, from the advantages of the high ability of MSNs to be used as a scaffold for efficient dye encapsulation and the magnetic nanoparticles as efficient biological carriers. Under optimal conditions, the fluorescence signal (The fluorescence of solutions was measured using a quartz fluorescence cell (PMT voltage:720, Ex wavelegth:540, Em wavelength:568, All measurements were carried out at room temperature) increased with the increment of HBsAg concentration in the linear dynamic range of 6.1 ag/ml to 0.012 ng/ml with a detection limit (LOD) of 5.7 ag/ml. The relative standard deviation, measured between the resulting fluorescence peaks was obtained by 6.0%.

The electrochemical detection of prostate specific antigen on glassy carbon electrode modified with combinations of graphene quantum dots, cobalt phthalocyanine and an aptamer

Herein, a novel aptasensor is developed for the electrochemical detection of prostate specific antigen (PSA) on electrode surfaces modified using various combinations of a Cobalt phthalocyanine (CoPc), an aptamer and graphene quantum dots (GQDs). Electrochemical impedance spectroscopy (EIS) as well as differential pulse voltammetry (DPV) are employed for the detection of PSA. In both analytical techniques, linear calibration curves were observed at a concentration range of 1.2-2.0 pM. The glassy carbon electrode where CoPc and GQDs are placed on the electrode when non-covalently linked followed by addition of the aptamer (GQDs-CoPc(ππ)-aptamer (sequential)) showed the best performance with a limit of detection (LoD) as low as 0.66 pM when using DPV. The detection limits were much lower than the dangerous levels reported for PSA in males tested for prostate cancer. This electrode showed selectivity for PSA in the presence of bovine serum albumin, glucose and L-cysteine. The aptasensor showed good stability, reproducibility and repeatability, deeming it a promising early detection device for prostate cancer.

Label-free Electrochemical Impedance Spectroscopy Aptasensor for Ultrasensitive Detection of Lung Cancer Biomarker Carcinoembryonic Antigen

In this work, an integrated electrode system consisting of a graphene working electrode, a carbon counter electrode and an Ag/AgCl reference electrode was fabricated on an FR-4 glass fiber plate by a polyethylene self-adhesive mask stencil method combined with a manual screen printing technique. The integrated graphene electrode was used as the base electrode, and AuNPs were deposited on the working electrode surface by cyclic voltammetry. Then, the carcinoembryonic antigen aptamer was immobilized using the sulfhydryl self-assembly technique. The sensor uses [Fe(CN)6]3-/4- as a redox probe for label free detection of carcinoembryonic antigen based on the impedance change caused by the difference in electron transfer rate before and after the binding of carcinoembryonic antigen aptamer and the target carcinoembryonic antigen. The results showed a good linear relationship when the CEA concentration is in the range of 0.2-15.0 ng/ml. The detection limit was calculated to be 0.085 ng/ml (S/N = 3).

Aptamer-based sensing of breast cancer biomarkers: a comprehensive review of analytical figures of merit

INTRODUCTION

Accurate determination of the aberrantly expressed biomarkers such as human epidermal growth factor receptor 2 (HER2), carcinoembryonic antigen (CEA), platelet-derived growth factor (PDGF), mucin 1 (MUC1), and vascular endothelial growth factor VEGF₁₆₅ have played an essential role in the clinical management of the breast cancer. Assessment of these cancer-specific biomarkers has conventionally relied on time-taking methods like the enzyme-linked immunosorbent assay and immunohistochemistry. However, recent development in the aptamer-based diagnostics has allowed developing tools that may substitute the conventional means of biomarker assessment in breast cancer. Adopting the aptamer-based diagnostic tools (aptasensors) to clinical practices will depend on their analytical performance on clinical samples.

AREAS COVERED

In this review, we provide an overview of the analytical merits of HER2, CEA, PDGF, MUC1, and VEGF₁₆₅ aptasensors. Scopus and Pubmed databases were searched for studies reporting aptasensor development for the listed breast cancer biomarkers in the past one decade. Linearity, detection limit, and response time are emphasized.

EXPERT OPINION

In our opinion, aptasensors have proven to be on a par with the antibody-based methods for detection of various breast cancer biomarkers. Though robust validation of the aptasensors on significant sample size is required, their ability to detect pathophysiological range of biomarkers suggest the possibility of future clinical adoption.

Biocatalyst and colorimetric biosensor of carcinoembryonic antigen constructed via chicken egg white-copper phosphate organic/inorganic hybrid nanoflowers

In this article, the dual-functional chicken egg white-copper phosphate organic-inorganic hybrid nanoflowers (Cu-NFs), combining the functions of signal amplification and biological recognition, were prepared through a simple one-pot method. The Cu-NFs exhibit excellent biocatalytic activity of peroxidase and polyphenol oxidase. Besides, a biotin-labeled secondary antibody encapsulated Cu-NFs-2 (Cu-NFs-2@Biotin-NHS-Ab₂) capture probe was prepared by using the interaction between avidin in the egg white and biotin. Based upon this superiority, the as-prepared Cu-NFs-2 were used in labeled avidin-biotin enzyme-linked immunosorbent assay (Cu-NFs-2 based-LAB-ELISA) to construct a sensitive colorimetric biosensor for the ultrasensitive detection of carcinoembryonic antigen (CEA). Under weak alkaline (pH = 7.5) conditions, the as-developed colorimetric sensor displayed a wide linear range of 0.05-40 ng/mL with a detection limit of 3.52 pg/mL. Furthermore, this colorimetric sensor has been successfully applied to the detection of CEA in human serum samples. Therefore, the as-developed colorimetric sensor has broad application prospects in the field of medical diagnosis and portable detection.

Techniques for Detection of Clinical Used Heparins

Heparins and sulfated polysaccharides have been recognized as effective clinical anticoagulants for several decades. Heparins exhibit heterogeneity depending on the sources. Meanwhile, the adverse effect in the clinical uses and the adulteration of oversulfated chondroitin sulfate (OSCS) in heparins develop additional attention to analyze the purity of heparins. This review starts with the description of the classification, anticoagulant mechanism, clinical application of heparins and focuses on the existing methods of heparin analysis and detection including traditional detection methods, as well as new methods using fluorescence or gold nanomaterials as probes. The in-depth understanding of these techniques for the analysis of heparins will lay a foundation for the further development of novel methods for the detection of heparins.

Rapid and simultaneous detection of heart-type fatty acid binding protein and cardiac troponin using a lateral flow assay based on metal organic framework@CdTe nanoparticles

Herein, a zirconium metal organic framework (ZrMOF) based lateral flow assay (LFA) is described for the qualitative analysis of early acute myocardial infarction (AMI) biomarkers including heart-type fatty acid binding protein (h-FABP) and cardiac troponin (cTnT). ZrMOF@CdTe nanoparticles (NPs) are synthesized by a simple hydrothermal method. By changing the hydrothermal reaction time, ZrMOF@CdTe NPs with different fluorescent colours can be obtained. They can emit different colours of fluorescence under the excitation of a single wavelength, which makes them suitable for multiplexed lateral flow assays (mLFA). The visual limit of detection of the ZrMOF@CdTe-based LFA for the h-FABP antigen is 1 μg L-1. The analysis can be completed within 8 min and has the advantages of being easy to operate and visual detection. A serum sample collected from patients is successfully detected using this LFA. This assay is widely applicable and simple, has strong anti-interference ability, and is cost-effective and can provide basic information for later treatment.

Multichannel Paper Chip-Based Gas Pressure Bioassay for Simultaneous Detection of Multiple MicroRNAs

Simultaneous detection of multi-biomarkers not only enhances the accuracy of disease diagnosis but also improves detection efficiency and reduces cost. It is vital to achieve portable, simple, low-cost, and simultaneous detection of biomarkers for point-of-care (POC) diagnostics in a low-resource setting. Herein, a multichannel paper chip-based gas pressure bioassay was developed for the simultaneous detection of multiple biomarkers by combining multichannel paper chips with a portable gas pressure meter. Four DNA tetrahedral probes (DTPs) were used as capture probes and were immobilized in different detection zones of the paper chips to improve hybridization efficiency and reduce nonspecific adsorption. The formation of a sandwich structure between target microRNAs (miRNAs), the capture probe, and platinum nanoparticles (PtNPs)-modified complementary DNA (PtNPs-cDNA) transformed biomolecular recognition into quantitative detection of gas pressure. Four lung cancer-related miRNAs were detected simultaneously by a portable gas pressure meter. There is a good linear relationship between gas pressure and the logarithm of miRNA concentration in the range of 10 pM to 100 nM. Compared with single-stranded DNA capture probe, the signal-to-noise (S/N) of DNA tetrahedral probes improved more than 3 times. Using ring-oven washing, the unbound reagents in all channels of the paper chip were simultaneously and continuously washed away, leading to a more cheap, simple, and fast separation than magnetic separation. Therefore, it offers a promising multichannel paper chip-based gas pressure bioassay for portable and simultaneous detection of multiple biomarkers.

A dual-mode label-free electrochemical immunosensor for ultrasensitive detection of procalcitonin based on g-C3N4-NiCo2S4-CNTs-Ag NPs

Herein, a label-free electrochemical immunosensor based on differential pulse voltammetry (DPV) and amperometric i-t curve (i-t) dual-mode analysis is proposed for early quantitative detection of procalcitonin (PCT). Due to the advantages of high chemical stability and biocompatibility, graphite carbon nitride (g-C₃N₄) was adopted as a high-capacity sensing interface to carry signal indicators. As an effective indicator of chronoamperometry, nickel cobalt sulfide (NiCo₂S₄) was uniformly dispersed on the surface of g-C₃N₄ through in-situ hydrothermal synthesis, which not only promotes the activation of bimetallic activity, but also effectively prevents the aggregation of NiCo₂S₄. At the same time, in order to establish a dual-mode analysis platform to improve accuracy and sensitivity, highly conductive carbon nanotubes (CNTs) were hybridized with composite materials to load Ag nanoparticles (Ag NPs), which have excellent oxidizing properties and are used as indicators of DPV. On account of this advanced sensing strategy, a wide linear response (DPV: 0.05 ng mL^-1-50 ng mL^-1 and i-t: 1.00 pg mL^-1-10.00 ng mL^-1) and a low detection limit (DPV: 16.70 pg mL^-1 and i-t: 0.33 pg mL^-1) are demonstrated. The immunosensor synthesized by this method has good stability and sensitivity, which could be applied in clinical diagnosis and treatment.

Paper-Based Enzymatic Colorimetric Assay for Rapid Malathion Detection

Due to their unique properties, paper-based biosensors have attracted attention as inexpensive devices for on-site analysis. To achieve fast and sensitive detection of analytes, immobilization of enzymes with high apparent activities on paper is highly desirable; however, this is challenging. Herein, we report an improved approach to attach a malathion degrading enzyme, PoOPH_M9, on paper via an interlocking network of Pluronic F127 (PF127)-poly(acrylic acid)-enzyme conjugates. The addition of PF127 improved retention of enzymatic activity as the apparent kinetic constant V_max of the immobilized enzyme increased two-fold compared with the paper prepared without PF127. The PF127-poly(acrylic acid)-PoOPH_M9 papers provided rapid colorimetric detection of malathion at 0.1-50 mM. The detection was completed within 5 min using a smartphone and image analysis software. As a proof-of-concept, malathion-contaminated water, plant, and apple samples were analyzed with the papers successfully. This material is promising for on-site rapid analysis of malathion-contaminated samples.

Laser engraved microapillary pump paper-based microfluidic device for colorimetric and electrochemical detection of salivary thiocyanate

A microcapillary grooved paper-based analytical device capable of dual-mode sensing (colorimetric and electrochemical detection) was demonstrated for analysis of viscous samples (e.g., human saliva). Herein, a hollow capillary channel was constructed via laser engraved micropatterning functions as a micropump to facilitate viscous fluidic transport, which would otherwise impede analysis on paper devices. Using salivary thiocyanate as a model analyte, the proposed device was found to exhibit a promising sensing ability on paper devices without the need for sample pretreatment or bulky instrumentation, as normally required in conventional methods used for saliva analysis. An extensive linear dynamic range covering detection of salivary thiocyanate for both high and trace level regimes (5 orders of magnitude working range) was collectively achieved using the dual-sensing modes. Under optimal conditions, the limit of detection was 6 μmol L^-1 with a RSD of less than 5%. An excellent stability for the μpumpPAD was also observed for over 30 days. Real sample analysis using the proposed device was found to be in line with the standard chromatographic method. Benefitting from simple fabrication and operation, portability, disposability, low sample volume (20 μL), and low cost (< 1 USD), the μpumpPAD is an exceptional alternative tool for the detection of various biomarkers in saliva specimens.

Biomedical application of mesoporous silica nanoparticles as delivery systems: a biological safety perspective

The application of mesoporous silica nanoparticles (MSNs) as drug delivery systems to deliver drugs, proteins, and genes has expanded considerably in recent years, using in vitro and animal studies. For future translation to clinical applications, the biological safety aspects of MSNs must be considered carefully. This paper reviews the biosafety of MSNs, examining key issues such as biocompatibility, effects on immune cells and erythrocytes, biodistribution, biodegradation and clearance, and how these vary depending on the effects of the physical and chemical properties of MSNs such as particle size, porosity, morphology, surface charge, and chemical modifications. The future use of MSNs as a delivery system must extend beyond what has been learnt thus far using rodent animal models to encompass larger animals.

Flexible paper-based label-free electrochemical biosensor for the monitoring of miRNA-21 using core-shell Ag@Au/GQD nano-ink: a new platform for the accurate and rapid analysis by low cost lab-on-paper technology

miRNA-21 is one of the most famous and prominent microRNAs that is important in the development and emergence of cancers. So, the sensitive and selective monitoring of miRNA-21 as a very common biomarker in cancer treatment is necessary. In this work, a novel paper-based electrochemical peptide nucleic acid (PNA) sensor was developed for the detection of miRNA-21 in human plasma samples by using Ag@Au core-shell nanoparticles electrodeposited on graphene quantum dots (GQD) conductive nano-ink (Ag@Au core-shell/GQD nano-ink), which was designed directly by writing pen-on paper technology on the surface of photographic paper. This nano-ink has a great surface area for biomarker immobilization. The prepared paper-based biosensor is very small and cheap, and also has high stability and sensitivity. Hybridization of PNA was measured using various electrochemical techniques, such as cyclic voltammetry (CV), square wave voltammetry (SWV) and chronoamperometry (ChA). FE-SEM (Field Scanning Electron Microscope), TEM (Transmission Electron Microscope), EDS and DLS (Dynamic Light Scattering) tests were performed to identify the engineering safety sensor. Under optimal conditions, the linear range for the calibration curve was from 5 pM to 5 μM, and the achieved LLOQ was 5 pM. The obtained results recommended that the proposed bioassay might be suitable for an early diagnosis of cancer based on the inhibition of the expression of miRNA-21, which activates the enzyme caspase and accelerates apoptotic proteins and death in tumor cells.

A light-up fluorescence resonance energy transfer magnetic aptamer-sensor for ultra-sensitive lung cancer exosome detection

In vitro liquid biopsy based on exosomes offers promising opportunities for fast and reliable detection of lung cancers. In this work, we present a fluorescence resonance energy transfer (FRET) magnetic aptamer-sensor for magnetic enrichment of exosomes with aptamers and detection of cancerous-surface proteins based on a light-up FRET strategy. Fluorescent quantum dots (QDs) and aptamers were introduced onto magnetic nanoparticles and the fluorescence emission turned down when the aptamers were paired with their complementary DNA on the surface of Au nanoparticles. Later, competitive binding of exosomes with the aptamers expelled the Au nanoparticles resulting in an exosome concentration-dependent linear increase of QD fluorescence intensity in a broad exosome concentration range (5 × 10²-5 × 10⁹ particles per mL). As found in our work, this system behaved ultra-sensitively and the calculated detection limit of this FRET magnetic aptamer-sensor was as low as 13 particles per mL. Furthermore, taking epithelial cancer-specific antigen (epithelial cell adhesion molecule, EpCAM) screening as a typical example, our built FRET magnetic aptamer-sensor allowed a rapid and efficient distinction of all the epithelial cancer cases (7 lung cancers and 5 other cancers) from health volunteers with 100% accuracy.

In situ monitoring of gating approach on mesoporous silica nanoparticles thin-film generated by the EASA method for electrochemical detection of insulin

An innovative label-free electrochemical aptasensing platform has been designed for detection of insulin using functionalized mesoporous silica thin-film (MSTF) coated on a glassy carbon electrode through the one-step electrochemically assisted self-assembly (EASA) method. This strategy is contingent upon the covalent attachment of a complementary DNA (cDNA) oligonucleotide sequence on the mesoporous silica surface, for which further hybridization with its labeled aptamer as a gating molecule restricts the diffusion of the electroactive probe (Fe(CN)₆^3-/4-) toward the electrode surface by the closing of mesochannels. Upon insulin introduction as the stimulus target molecule, hybridization between aptamer and cDNA is efficiently destroyed, which triggers the opening of nanochannels to facilitate redox probe diffusion toward the electrode with a noticeable increase in differential pulse voltammetry signal. The proposed aptasensor showed a wide detection ranging from 10.0 to 350.0 nM and a suitable detection limit of 3.0 nM. This method offers the sensitive and rapid detection of insulin without the need for cargo (dye/fluorophore) as an electrochemical marker inside the pore, at low cost and with a fast modification time.

Photoluminescence-based immunochemical methods for determination of C-reactive protein and procalcitonin

Modern, sensitive, rapid, and selective analytical methods for the detection of inflammatory markers are a crucial tool for the assessment of inflammation state, efficacy of medical intervention, and the prediction of future diseases. Their development requires understanding of current state for point-of-care testing of inflammatory markers and identification of their crucial drawbacks. This review summarizes the progress in the application of luminescent labels for immunoassays. The luminescent labels became more popular in the latest decade due to their high sensitivity, selectivity, and robustness. This review presents a constructive analysis of different luminescent labels such as fluorescent organic dyes, quantum dots, long-lived emissive nanoparticles, and up-converting nanocrystals, as well as a range of the strategies for inflammatory markers determination. The advantages and disadvantages of all classes of luminescent labels are demonstrated, and the strategies of labels modification for their improvement are discussed. The current approaches for the creation of luminescent probes and robust assays are also highlighted.

Integrating Near-Infrared Visual Fluorescence with a Photoelectrochemical Sensing System for Dual Readout Detection of Biomolecules

Compared with traditional visible light-driven fluorescence visualization (FV), near-infrared (NIR)-induced FV is an interesting and promising method, while photoelectrochemical (PEC) immunoassay sensing possesses the advantages of high sensitivity, low cost, and simple instrumentation. We combined PEC sensing with NIR-induced FV together and developed a dual readout sensing platform. In this protocol, based on the antibody-analyte (i.e., antigen, DNA, and RNA) reaction and the sandwich-type structure, CuInS₂ microflowers as the matrix provided the original background photocurrent; chlorin e6 (Ce6) was conjugated to antibody-modified upconversion nanoparticles and formed a signal label for the PEC sensing and naked-eye readout. Different from traditional PEC immunosensors, under NIR illumination, the developed dual mode sensing platform could achieve quick qualitative analysis and quantitative analysis. Preliminary application performance of the proposed biosensor in prostate-specific antigen analysis is acceptable, indicating its promising potential in clinical/biological studies.

Aptamer-based fluorescent sensors for the detection of cancer biomarkers

Aptamers are short single-stranded RNA or DNA molecules that can recognize a series of targets with high affinity and specificity. Known as "chemical antibodies", aptamers have many unique merits, including ease of chemical synthesis, high chemical stability, low molecular weight, lack of immunogenicity, and ease of modification and manipulation compared to their protein counterparts. Using aptamers as the recognition groups, fluorescent aptasensors provide exciting opportunities for sensitive detection and quantification of analytes. Herein, we give an overview on the recent development of aptamer-based fluorescent sensors for the detection of cancer biomarkers. Based on various nanostructured sensor designs, we extended our discussions on sensitivity, specificity and the potential applications of aptamer-based fluorescent sensors in early diagnosis, treatment and prognosis of cancers.

Nanostructures for Biosensing, with a Brief Overview on Cancer Detection, IoT, and the Role of Machine Learning in Smart Biosensors

Biosensors are essential tools which have been traditionally used to monitor environmental pollution and detect the presence of toxic elements and biohazardous bacteria or virus in organic matter and biomolecules for clinical diagnostics. In the last couple of decades, the scientific community has witnessed their widespread application in the fields of military, health care, industrial process control, environmental monitoring, food-quality control, and microbiology. Biosensor technology has greatly evolved from in vitro studies based on the biosensing ability of organic beings to the highly sophisticated world of nanofabrication-enabled miniaturized biosensors. The incorporation of nanotechnology in the vast field of biosensing has led to the development of novel sensors and sensing mechanisms, as well as an increase in the sensitivity and performance of the existing biosensors. Additionally, the nanoscale dimension further assists the development of sensors for rapid and simple detection in vivo as well as the ability to probe single biomolecules and obtain critical information for their detection and analysis. However, the major drawbacks of this include, but are not limited to, potential toxicities associated with the unavoidable release of nanoparticles into the environment, miniaturization-induced unreliability, lack of automation, and difficulty of integrating the nanostructured-based biosensors, as well as unreliable transduction signals from these devices. Although the field of biosensors is vast, we intend to explore various nanotechnology-enabled biosensors as part of this review article and provide a brief description of their fundamental working principles and potential applications. The article aims to provide the reader a holistic overview of different nanostructures which have been used for biosensing purposes along with some specific applications in the field of cancer detection and the Internet of things (IoT), as well as a brief overview of machine-learning-based biosensing.

Label free, electric field mediated ultrasensitive electrochemical point-of-care device for CEA detection

Developing point-of-care (PoC) diagnostic platforms for carcinoembryonic antigen detection is essential. However, thefew implementations of transferring the signal amplification strategies in electrochemical sensing on paper-based platforms are not satisfactory in terms of detection limit (LOD). In the quest for pushing down LOD, majority of the research has been targeted towards development of improved nanostructured substrates for entrapping more analyte molecules and augmenting the electron transfer rate to the working electrode. But, such approaches have reached saturation. This paper focuses on enhancing the mass transport of the analyte towards the sensor surface through the application of an electric field, in graphene-ZnO nanorods heterostructure. These hybrid nanostructures have been deposited on flexible polyethylene terephthalate substrates with screen printed electrodes for PoC application. The ZnO nanorods have been functionalized with aptamers and the working sensor has been integrated with smartphone interfaced indigenously developed low cost potentiostat. The performance of the system, requiring only 50 µl analyte has been evaluated using electrochemical impedance spectroscopy and validated against commercially available ELISA kit. Limit of detection of 1 fg/ml in human serum with 6.5% coefficient of variation has been demonstrated, which is more than three orders of magnitude lower than the existing attempts on PoC device.

Polyaniline@Au organic-inorganic nanohybrids with thermometer readout for photothermal immunoassay of tumor marker

A photothermal immunoassay using a thermometer as readout based on polyaniline@Au organic-inorganic nanohybrids was built. Temperature output is acquired due to the photothermal effect of the photothermal nanomaterial. Polyaniline@Au organic-inorganic nanohybrids were synthesized by interfacial reactions with high photothermal conversion efficiency. A sandwich structure of the immunocomplex was prepared on a microplate for determination of carcinoembryonic antigen (CEA) by polyaniline@Au organic-inorganic nanohybrids as nanolabel. The released heat based on light-to-heat conversion from the photothermal nanolabel under NIR irradiation is detectable using the thermometer. The increased temperature is directly proportional to CEA concentration. The linear range of the photothermal immunoassay is 0.20 to 25 ng mL-1 with determination limit of 0.17 ng mL-1. Polyaniline@Au organic-inorganic nanohybrids with high photothermal conversion efficiency was synthesized as labels to construct photothermal immunosensor. The sandwich-type immunoassay was built on 96 hole plate based on specific binding of antigen and antibody. Carcinoembryonic antigen in sample was detected quantitatively by thermometer readout.

Dual-Mode Aptasensor Assembled by a WO3/Fe2O3 Heterojunction for Paper-Based Colorimetric Prediction/Photoelectrochemical Multicomponent Analysis

The programed bimodal photoelectrochemical (PEC)-sensing platform based on DNA structural switching induced by targets binding to aptamers was innovatively designed for the simultaneous detection of mucin 1 (MUC1) and microRNA 21 (miRNA-21). To promote excellent current intensity as well as enhance the sensitivity of aptasensors, the evenly distributed WO₃/Fe₂O₃ heterojunction was prepared as a transducer material, notably reducing the background signal response and extending the absorption of light. The multifunctional paper-based biocathode was assembled to provide a visual colorimetric assay. When introducing the integrated signal probe (ISP) composed of signal probe 1 (sP1) and signal probe 2 (sP2) on paper-based working units modified with gold nanoparticles (AuNPs), recognition sites of two targets were formed. In the presence of MUC1 protein, both sP1 and the target on the working unit were released into the corresponding colorimetric unit because of the DNA specific recognition. The horseradish peroxidase-streptavidin (HRP-SA) carried by free sP1 could oxidize 3,3',5,5'-tetramethylbenzidine (TMB) to turn a blue-colored oxidized TMB (oxTMB) in the presence of hydrogen peroxide (H₂O₂), which ultimately gained a higher photocurrent signal. Furthermore, miRNA-21 was modified on another working unit by binding with sP2, leading to changes in the current signal and thus enabling real-time detection of analytes with the assistance of a digital multimeter. The PEC aptasensor offered a wide dynamic range of 10 fg·mL^-1-100 ng mL^-1 for MUC1 and 0.1 pM-10 nM for miRNA-21, with a low detection limit of 3.4 fg·mL^-1 and 36 fM, respectively. It laid the foundation for synchronous detection of multiple analytes and initiated a new way for the enhancement in modern next-generation disease diagnosis.

Handheld pH meter-assisted immunoassay for C-reactive protein using glucose oxidase-conjugated dendrimer loaded with platinum nanozymes

A simple and feasible pH meter-based immunoassay is reported for detection of C-reactive protein (CRP) using glucose oxidase (GOD)-conjugated dendrimer loaded with platinum nanozyme. Initially, platinum nanozymes were loaded into the dendrimers through an in situ synthetic method. Then, GOD and monoclonal anti-CRP antibody with a high molar ratio were covalently conjugated onto carboxylated dendrimers via typical carbodiimide coupling. The immunoreaction was carried out with a competitive mode in a CRP-coated microplate. Along with formation of immunocomplex, the added glucose was oxidized into gluconic acid and hydrogen peroxide by GOD, and the latter was further decomposed by platinum nanozyme, thus accelerating chemical reaction in the positive direction. The produced gluconic acid changed the pH of detection solution, which was determined using a handheld pH meter. Under optimum conditions, the pH meter-based immunoassay gave a good signal toward target CRP from 0.01 to 100 ng mL-1. The limit of detection was 5.9 pg mL-1. An intermediate precision ≤ 11.2% was acquired with batch-to-batch identification. No nonspecific adsorption was observed during a series of procedures to detect target CRP, and the cross-reaction against other biomarkers was very low. Importantly, our system gave well-matched results for analysis of human serum samples relative to a referenced ELISA kit.Graphical abstract.

Prussian blue-doped PAMAM dendrimer nanospheres for electrochemical immunoassay of human plasma cardiac troponin I without enzymatic amplification

Rapid and accurate identification of cardiac troponin I (cTnl) in biological fluids is very essential for judging acute myocardial infarction (AMI).

Optical detection of sulfur mustard contaminated surfaces based on a sprayable fluorescent probe

A water-based sprayable functional polymer was immobilized with the fluorescent probe DPXT and was used as a chemo-sensor for rapid localization of surface contamination by sulfur mustard.

Luminescent Nanomaterials (II)

In this review, we focus on sensing techniques and biological applications of various luminescent nanoparticles including quantum dot (QD), up-conversion nanoparticles (UCNPs) following the previous chapter. Fluorescent phenomena can be regulated or shifted by interaction between biological targets and luminescence probes depending on their distance, which is so-called Fӧrster resonance energy transfer (FRET). QD-based FRET technique, which has been widely applied as a bioanalytical tool, is described. We discuss time-resolved fluorescence (TRF) imaging and flow cytometry technique, using photoluminescent nanoparticles with unique properties for effectively improving selectivity and sensitivity. Based on these techniques, bioanalytical and biomedical application, bioimaging with QD, UCNPs, and Euripium-activated luminescent nanoprobes are covered. Combination of optical property of these luminescent nanoparticles with special functions such as drug delivery, photothermal therapy (PTT), and photodynamic therapy (PDT) is also described.

Surface-enhanced electrochemiluminescence combined with resonance energy transfer for sensitive carcinoembryonic antigen detection in exhaled breath condensates

The detection of biomarkers in exhaled breath condensates (EBCs) is regarded as a promising non-invasive diagnostic approach. However, the ultralow concentration of biomarkers in EBCs is a great challenge. Herein, a sensitive dual signal amplification strategy was developed based on surface-enhanced electrochemiluminescence (SEECL) combined with resonance energy transfer (RET). Gold nanoparticles-functionalized graphite-like carbon nitride nanohybrids (Au-g-C₃N₄ NHs) could be used as an energy transfer donor because of the good overlap between its emission peak and the absorption peak of tris(2,2'-bipyridine)ruthenium dichloride (Ru(bpy)₃Cl₂) at 460 nm. Gold-silicon dioxide core-shell nanoparticles doped with Ru(bpy)₃²⁺(Au@SiO₂-Ru) were employed as an energy transfer acceptor emitting at 620 nm. Moreover, the signals at 620 nm emitted by Ru (bpy)₃²⁺ were enhanced by 5 times, attributed to the localized surface plasmon resonance (LSPR) of gold nanoparticles (Au NPs). The detection of carcinoembryonic antigen (CEA) was performed by using two aptamers as the recognition unit; whereby aptamer 1 (Apt1) was modified on the surface of Au-g-C₃N₄ NHs, and aptamer 2 (Apt2) was banded on the surface of Au@SiO₂-Ru. In the presence of CEA, a sandwich structure was formed between Au-g-C₃N₄ NHs-Apt1-CEA and Apt2-Au@SiO₂-Ru, which resulted in an ultrasensitive detection of CEA. The proposed electrochemiluminescence sensor showed a wide linear relationship with the CEA concentration in the range from 1.0 pg mL^-1 to 5.0 ng mL^-1, with a limit of detection (LOD) of 0.3 pg mL^-1. Finally, the practicality of the proposed sensor was demonstrated to detect CEA in EBCs, and the obtained results were in good agreement with the enzyme-linked immunosorbent assay (ELISA) method.

Facile and rapid synthesis of emission color-tunable molybdenum oxide quantum dots as a versatile probe for fluorescence imaging and environmental monitoring

Recent years have seen molybdenum oxide quantum dots (MoOx QDs) as a booming material due to their attractive physical and chemical properties. However, there is still a large demand for MoOx QDs with long-wavelength emission by a facile strategy but these are more challenging to obtain. Herein, we rationally designed and successfully prepared nitrogen and phosphorus co-doped green emitting MoOx QDs (N,P-MoOx QDs) through a microwave-assisted rapid method. They exhibit a maximum emission at 500 nm under a 430 nm excitation. Moreover, by controlling their sizes in the process, we find that such a strategy enables the tuning of the emission color of N,P-MoOx QDs from green to blue. N,P-MoOx QDs show a significant fluorescence response to pH changes, and also display pH-sensitive near-infrared localized surface plasmon resonance (LSPR) at 866 nm. An effective and simple pH probe with a dual-signal response is achieved using N,P-MoOx QDs. As environmental sensors, N,P-MoOx QDs can be applied for sensitive detection of the concentrations of permanganate and captopril, offering the linear range from 0.08 to 25 μM and 0.1 to 31 μM, respectively. Benefitting from the effect of doping nitrogen and phosphorus, the probe could detect a wide range of pH changes (2-9) and is endowed with superior biocompatibility. Further, it is successfully used to "see" the intracellular pH variation by fluorescence confocal imaging. These findings not only demonstrate the achievement of a promising multifunctional probe for biosensing and environmental detection, but also pave the way for the fabrication of transition metal oxide QDs with tunable optical properties.

Distance-dependent visual fluorescence immunoassay on CdTe quantum dot-impregnated paper through silver ion-exchange reaction

A paper-based visual fluorescence immunoassay is presented for the detection of matrix metalloproteinase-7 (MMP7) that is related to renal cancer. The method is based on the distance-dependent fluorescence quenching of CdTe quantum dots (QDs) on a nitrocellulose membrane by Ag⁺ following a sandwich-type immunoreaction on microtiter wells using silver nanoparticle (AgNP)-labeled secondary antibody- and primary antibody-coated microtiter wells. The silver nanoparticles captured in the well are dissolved with HNO₃, while the quenching effect of QDs is based on silver ion-exchange reaction under 365-nm excitation light irradiation. Increasing concentration of released Ag⁺, thus higher concentration of the protein, leads to an increased distance of quenching on the nitrocellulose membrane. The paper-based immunoassay by combination of AgNP-assisted ion-exchange reaction with QD gives good distance-dependent responses and allows the detection of MMP7 at a concentration as low as 7.3 pg mL^-1. The coefficients of variation are less than 6.9% and 12.4% for intra-assay and inter-assay, respectively. High specificity and long-term stability are achieved during the assay. Importantly, the testing of human serum samples using our strategy shows well-matched results with commercial human MMP7 ELISA kits. Graphical abstract A distance-dependent visual immunoassay is developed for the determination of serum matrix metalloproteinase-7 on CdTe quantum dot-impregnated paper with silver ion-exchange reaction.

Cable-Like Core-Shell Mesoporous SnO2 Nanofibers by Single-Nozzle Electrospinning Phase Separation for Formaldehyde Sensing

In this study, we have developed a simple and efficient single-nozzle electrospinning strategy involving the phase separation of polystyrene and poly(vinylpyrrolidone) to construct cable-like core-shell mesoporous SnO₂ nanofibers. Compared with traditional multi-axial electrospinning approaches to the synthesis of core-shell nanofibers, the single-nozzle electrospinning process requires no complex multi-axial electrospinning setups or post-treatments, just drying and annealing after electrospinning. The obtained SnO₂ nanofibers show promise as a sensing material for formaldehyde at low concentrations, the detection limit being about 1 ppm. Furthermore, the nanofibers exhibited good cycling stability and selectivity, with response and recovery times toward 10 ppm formaldehyde being approximately 18 and 196 s, respectively, at an operating temperature of 195 °C.

Highly sensitive detection of carcinoembryonic antigen using copper-free click chemistry on the surface of azide cofunctionalized graphene oxide

In this study, we reported a highly sensitive method for detecting carcinoembryonic antigen (CEA) based on an azide cofunctionalized graphene oxide (GO-N₃) and carbon dot (CDs) biosensor system. Carbon dots-labeled DNA (CDs-DNA) combined with GO-N₃ using copper-free click chemistry (CFCC), which quenched the fluorescence of the CDs via fluorescence resonance energy transfer (FRET). Upon the addition of CEA, fluorescence was recovered due to the combination of CEA and aptamer. Under optimal conditions, the relative fluorescence intensity was linear with CEA concentration in the range of 0.01-1 ng/mL (R² = 0.9788), and the limit of detection (LOD) was 7.32 pg/mL (S/N = 3). This biosensor had a high sensitivity and good selectivity for CEA detection in serum samples, indicating that the novel sensor platform holds a great potential for CEA and other biomarkers in practical applications.

Fluorescent AgInS/ZnS quantum dots microplate and lateral flow immunoassays for folic acid determination in juice samples

A noninstrumental rapid test for folic acid (FA) detection with visual results evaluation utilizing bright water-stable AgInS/ZnS (AIS/ZnS) quantum dots (QDs) is reported . AIS/ZnS QDs are hydrophilic photostable nanocrystals with size < 7 nm and emission in the visible range. They were synthesized directly in the water phase by a simple method compared to the synthesis of other QDs and conjugated with monoclonal antibodies specific for FA via ligand carboxyl groups. The conjugate was used for the development of instrumental qualitative and rapid quantitative FA detection methods. The competitive fluorescent microplate immunosorbent assay provided a limit of detection of 0.1 ng/mL FA and half maximal inhibitory concentration (IC₅₀) of 24 ng/mL FA. The analytical signal was measured at ʎ_ex = 410 nm and ʎ_em=590 nm. The proposed method showed no cross-reaction with other group B vitamins. For FA screening in juice samples, the lateral flow immunoassay was developed with a visual cutoff level of 3 μg/mL. In our perception, the developed methods are convenient for proving the perception of the AIS/ZnS QDs application as a luminescent label for immunoassay and are effective for FA detection. Graphical abstract.