Signal Tags Research Articles

A Turn-Off Fluorescent Biomimetic Sensor Based on a Molecularly Imprinted Polymer-Coated Amino-Functionalized Zirconium (IV) Metal-Organic Framework for the Ultrasensitive and Selective Detection of Trace Oxytetracycline in Milk.

Developing sensitive and effective methods to monitor oxytetracycline residues in food is of great significance for maintaining public health. Herein, a fluorescent sensor (NH2-UIO-66 (Zr)@MIP) based on a molecularly imprinted polymer-coated amino-functionalized zirconium (IV) metal-organic framework was successfully constructed and first used for the ultrasensitive determination of oxytetracycline. NH2-UIO-66 (Zr), with a maximum emission wavelength of 455 nm under 350 nm excitation, was prepared using a microwave-assisted heating method. The NH2-UIO-66 (Zr)@MIP sensor with specific recognition sites for oxytetracycline was then acquired by modifying a molecularly imprinted polymer on the surface of NH2-UIO-66 (Zr). The introduction of NH2-UIO-66 (Zr) as both a signal tag and supporter can strengthen the sensitivity of the fluorescence sensor. Thanks to the combination of the unique characteristics of the molecularly imprinted polymer and NH2-UIO-66 (Zr), the prepared sensor not only exhibited a sensitive fluorescence response, specific identification capabilities and a high selectivity for oxytetracycline, but also showed good fluorescence stability, satisfactory precision and reproducibility. The fabricated sensor displayed a fluorescent linear quenching in the OTC concentration range of 0.05-40 μg mL-1, with a detection limit of 0.012 μg mL-1. More importantly, the fluorescence sensor was finally applied for the detection of oxytetracycline in milk, and the results were comparable to those obtained using the HPLC approach. Hence, the NH2-UIO-66 (Zr)@MIP sensor possesses great application potential for the accurate evaluation of trace oxytetracycline in dairy products.

In situ formed carbon nanoparticles enables colorimetric and fluorometric dual-mode immunoassay detection of amantadine in poultry foodstuffs

To prevent the hazard concerns of amantadine (AMD) on humans, a sensitive and reliable detection method is urgently required. Herein, we reported a one-pot method in situ synthesis of carbon nanoparticles (CNPs) exhibited yellow color and green fluorescence. 4-Aminophenyl phosphate was catalyzed by alkaline phosphatase (ALP) to ρ-aminophenol (AP), and induced polymerization with diethylenetriamine (DETA) under a mild condition, which promotes in situ formation of CNPs with excellent photoluminescence stability. According to ALP-triggered specific catalytic reaction and in situ formed CNPs as signal tags, we proposed a dual-signal immunoassay for colorimetric and fluorometric monitoring AMD residues in poultry foodstuffs. Under an optimized detection parameter, the linear range and detection limit corresponded to colorimetric and fluorometric were 0.03 to 200 ng g−1 and 0.03 to 200 ng g−1, 0.047 ng g−1 and 0.060 ng g−1, respectively. The convincing performance of our established in-situ dual-readout sensing platforms opened a promising horizon for monitoring AMD residues in poultry productions.

Unique Electron-Transfer-Mediated Electrochemiluminescence of AuPt Bimetallic Nanoclusters and the Application in Cancer Immunoassay.

Noble Metal nanoclusters (NCs) are promising electrochemiluminescence (ECL) emitters due to their amazing optical properties and excellent biocompatibility. They have been widely used in the detection of ions, pollutant molecules, biomolecules, etc. Herein, we found that glutathione-capped AuPt bimetallic NCs (GSH-AuPt NCs) emitted strong anodic ECL signals with triethylamine as co-reactants which had no fluorescence (FL) response. Due to the synergistic effect of bimetallic structures, the ECL signals of AuPt NCs were 6.8 and 94 times higher than those of monometallic Au and Pt NCs, respectively. The electric and optical properties of GSH-AuPt NCs differed from those of Au and Pt NCs completely. An electron-transfer mediated ECL mechanism was proposed. The excited electrons may be neutralized by Pt(II) in GSH-Pt and GSH-AuPt NCs, resulting in the vanished FL. Furthermore, abundant TEA radicals formed on the anode contributed electrons to the highest unoccupied molecular orbital of GSH-Au2.5Pt NCs and Pt(II), booming intense ECL signals. Because of the ligand effect and ensemble effect, bimetallic AuPt NCs exhibited much stronger ECL than GSH-Au NCs. A sandwich-type immunoassay for alpha fetoprotein (AFP) cancer biomarkers was fabricated with GSH-AuPt NCs as signal tags, which displayed a wide linear range from 0.01 to 1000 ng·mL-1 and a limit of detection (LOD) down to 1.0 pg·mL-1 at 3S/N. Compared to previous ECL AFP immunoassays, this method not only had a wider linear range but also a lower LOD. The recoveries of AFP in human serum were around 108%, providing a wonderful strategy for fast, sensitive, and accurate cancer diagnosis.

Dual-Mode Paper Biosensing Platform Based on Oxidase-Like CoFeMn Nanozymes for Point-of-Care Detection of Glutathione

A paper-based biosensing platform is a point-of-care (POC) analysis toolkit for detection of various biomarkers. Nonetheless, its lack of high sensitivity, selectivity, and multi-signal readout poses a high degree of challenge. Herein, we introduce an interesting colorimetric-temperature dual-signal readout biosensor based on multifunctional CoFeMn biomimetic oxidase. Due to the cost-effectiveness, no additional detector requirement, dual-signal readout capacity, and darker signal change, CoFeMn hydroxide is innovatively fabricated by a facile hydrothermal method using Mn as an active center to construct a multifunctional signal tag for mimicking the structure of oxidase. This strategy allows CoFeMn hydroxide to exhibit an unusual oxidase-like activity, transforming O2 into ·OH in the absence of H2O2 and resulting in the generation of a colorimetric temperature dual signal by oxidizing 3,3′,5,5′-tetramethylbenzidine (TMB). We used glutathione (GSH) as the analyst and successfully applied this biosensor to determine GSH, which showed excellent analytical performance of rapidity, high specificity, sensitivity, and accuracy. Employing the colorimetric and temperature test strips, these toolkits are designed to visualize GSH. Benefiting from a relatively independent signal transduction pathway, the constructed test strip POC devices display satisfactory coupling efficiency and are further employed to monitor GSH in tumor cells. This research will be conducive to the rational design of a mimetic oxidase-based dual-response nanoprobe in paper-based POC devices, the exploration of more nanomaterial-derived mimetic oxidase, and the extension of their applications in medical diagnosis.

Dual-label vertical flow-based electrochemical immunosensor for rapid and simultaneous detection of hepatitis B surface and e virus antigens

The detection of hepatitis B virus (HBV)-associated biomarkers, especially hepatitis B surface (HBsAg) and hepatitis B e (HBeAg) antigens, is of critical significance for the early diagnosis and monitoring of disease progression. However, the detection of these biomarkers has seldom been reported. Herein, we first present a dual-label electrochemical vertical flow-based immunosensor (DL-eVFIS) for the simultaneous detection of HBsAg and HBeAg. DL-eVFIS was engineered to integrate multiple time-sequenced detection procedures into a single device, thus considerably shortening the overall assaying time to 6 min. To enable simultaneous determination, thionine (Th) and ferrocenecarboxylic acid (Fc) were employed as signal tags, as they demonstrate nonoverlapping specific reduction peaks. The appearance of target antigens resulted in a substantial increase in the electrochemical signal response of the redox tags. While requiring only a miniscule sample volume (5 µL), superior performance was achieved in terms of their limits of detection (LODs) at 1.66 pg/mL for HBsAg and 5.32 pg/mL for HBeAg. DL-eVFIS further demonstrates excellent specificity and selectivity in clinical sample analysis compared with the conventional method. This study contributes to next-generation point-of-care (POC) testing devices for HBV diagnosis and a wide range of biosensing applications.

A three-site recognition cytosensor based on multi-active AuIrPt polyhedral nanozymes for detection of CTCs

We developed a novel electrochemical cytosensor based on AuIrPt nanozymes and three-site recognition strategy for the detection of specific CTCs. Using pluronic F127 as the organic framework, new trimetallic AuIrPt nanozymes with exceptional multiple enzyme-like activities were synthesized, which could mimic the activities of three enzymes, SOD, POD, and CAT. Nanozymes linked with EpCAM (Epithelial cell adhesion molecule) aptamers served as signal tags to enhance sensitivity of the cytosensor, and anti-MUC1 (Mucin 1) and anti-EGFR (Epidermal growth factor receptor) antibodies for isolation and capture of the target CTCs, respectively. The AuIrPt nanozymes could approach the sensing interface and generate obvious currents through their exceptional catalytic activity only when all three proteins (MUC1, EpCAM, and EGFR) were simultaneously expressed on the cell membrane. Benefiting from the aforementioned advantages, our cytosensor could accurately distinguish between target cells and other cancer cells with a wide concentration range from 5 to 1 × 106 cells mL−1 and a low detection limit of 2 cells mL−1. Notably, the biosensor could assay target CTCs in complex whole blood matrixes, validating its resistance to interference and utility. By combining catalytic nanomaterials and three-site recognition strategy, a sensitive, accurate, and stable novel sensing platform has been developed, promising to facilitate the application of CTCs in early cancer screening.

A universal ratiometric method for Micro-RNA detection based on the ratio of electrochemical/electrochemiluminescence signal, and toehold-mediated strand displacement amplification

An ultra-selective and reproductive ratiometric platform was introduced based on the ratio of Ru(phen)32+ electrochemiluminescence (ECL) signal and methylene blue (MB) electrochemistry (EC) signal, which was amplified using a specific and efficient toehold-mediated strand displacement (TMSD). The stable DNA nanoclews (NCs) were efficiently loaded with MB (MB-NCs) as EC signal tags after being synthesized utilizing a simple rolling circle amplification reaction. Besides, Ti3C2-based nanocomposite could apply as a superb carrier for both Ru(phen)32+ and gold nanoparticles (Ti3C2–Au–Ru), resulting in a nearly constant ECL internal reference to eliminate the possible interferences. The Ti3C2–Au–Ru was attached to the surface of the electrode using Nafion, which exhibited excellent conductivity, and hairpin DNAs (hDNAs) were fixed on AuNPs via an Au–S bond. The designed biosensor was finally applied for miRNA-18a detection as a target model.The TMSD method made it possible to concurrently convert and amplify a single miRNA-18ainput into a large amount of output DNAs with high selectivity. These output DNAs were designed to unfold the stem-locked area of hDNAs. The opened hDNAs then hybridized with the MB-NCs to produce an EC signal. In the proposed biosensing system, by raising the target concentration of miRNA, the EC signal gradually rose, the ECL signal remained nearly constant, and the ratiometric detection method markedly promoted biosensor accuracy. Linear correlations of the ratio value of the EC/ECL with miRNA-18a concentrations between 20 aM and 50 pMwere observed, with the limit of detection of 9 aM. The biosensor was applied to detect miRNA-18a in real serum samples with satisfactory results.

Recent progress on nanozymes in electrochemical sensing

Nanozymes, as emerging artificial enzymes with superior catalytical properties and high stability, have attracted broad attention in the sensing field. As an important branch, nanozyme-based electrochemical sensing experienced fast growth in the last few years in combination with the intrinsic enzyme-mimic activity and unique physicochemical features owing to the high sensitivity, excellent selectivity, ease for miniaturization and versatile signal reporting modes. Generally, the electrochemical sensing can be achieved using nanozymes as signal tags for amplification or as the advanced catalysts for generating/influencing the electroactive probes. To highlight the achievement in this field, the representative works based on different signal reporting manners including traditional electrochemical assays and the evolutionary modes of electrochemiluminescent and photoelectrochemical sensing are discussed in details in the present work. Finally, the current challenges and perspectives facing are given.

A sandwich electrochemical immunosensor based on MXene@dual MOFs for detection of tumor marker CA125.

The detection signal of carbohydrate antigen 125 (CA125) can be quantitatively amplified via the dual metal-organic framework (MOF) sandwich strategy. We propose a versatile method for synthesizing uniform MXene and MIL-101(Fe)-NH2 composites that combine the advantages of both materials to build a base layer with superb performance. MXene exhibits excellent electrical conductivity and high surface area. The mesoporous MIL-101(Fe)-NH2 not only increases the loading capacity of the primary antibody but also possesses the catalytic activity of the metal center (Fe). UiO66 loaded with methylene blue (MB) was fabricated as an electrochemical immunosensor signal tag to enable the detection of CA125. The mixture of MXene and MIL-101(Fe)-NH2 prepared as the substrate was fixed by chitosan rich in amino groups. As the signal amplification sector, UiO66@MB enhanced secondary antibody loading capacity and generated a redox signal enabling the detection of antigenic substances. The proposed electrochemical immunosensor demonstrated high sensitivity with a low limit of detection (LOD) of 0.006 U/mL. Therefore, the dual MOF sandwich-based immunosensor provides a novel method for the early diagnosis of CA125.

Dual-Mode Biosensor for Simultaneous and Rapid Detection of Live and Whole Salmonella typhimurium Based on Bioluminescence and Fluorescence Detection.

Both live and dead Salmonella typhimurium (S.T) are harmful to human health, but there are differences in pathological mechanism, dosage, and security. It is crucial to develop a rapid and simultaneous assay to distinguish and quantify live and dead S.T in foods. Herein, one dual-mode biosensor for simultaneous detection of live and dead S.T was fabricated based on two phage probes, using portable bioluminescence and fluorescent meter as detectors, respectively. Firstly, a magnetic phage capture probe (M-P1) and a phage signal tag (P2-S) labeled with SYTO 13 fluorescent dye were prepared, respectively. Both M-P1 and P2-S can specifically conjugate with S.T to form a magnetic sandwich complex. After magnetic separation, the isolated complex can emit a fluorescent signal under an excited 365 nm laser, which can reflect the total amount of S.T. Afterwards, the lysozyme was added to decompose the captured live S.T, which can release ATP and produce a bioluminescent signal corresponding to the live S.T amount. The dead S.T concentration can be deduced by the difference between total and live examples. The detection limit of 55 CFU/mL for total S.T and 9 CFU/mL for live ones was within 20 min. The assay was successfully employed in milk samples and prospectively for on-site screening of other dead and live bacteria, while changing the phages for the targets.

Construction of an electrochemical immunosensor based on the OER signal of Au@CoFe-(oxy)hydroxide for ultrasensitive detection of CEA

Carcinoembryonic antigen (CEA) is a group of glycoproteins highly associated with cell adhesion and is an important antigen as a tumor biomarker commonly used in clinical diagnosis. Therefore, CEA detection plays a significant role in early clinical tumor diagnosis. In this study, an electrocatalytic signal labeled immunosensor was constructed for CEA ultrasensitive detection. We use a core–shell Au@CeO2 modified glassy carbon electrode (GCE) to capture more primary antibody (Ab1). The core–shell structure captures Ab1 through Au-S and OC–O bonds, providing more binding sites and a more stable binding force for Ab1. Because of the large specific surface area of the Au@CoFe-(oxy)hydroxide nanosheets and its outstanding oxygen evolution reaction (OER) signal under neutral medium, Au@CoFe-(oxy)hydroxide combined with secondary antibody (Ab2) as the signal tag and signal amplifier of the sensor. The proposed electrochemical immunosensor exhibited a good linear response from 0.0001 ng mL−1 to 200 ng mL−1 and a low detection limit of 0.0534 pg mL−1. The effectiveness of the sensor is verified by the standard addition method. This work provides a novel research approach for the clinical detection of tumor markers.

Target-induced Strand Displacement-based Electrochemical Aptasensor for the Determination of Tobramycin in Milk by Differential Pulse Voltammetry (DPV)

A target-induced strand displacement (TISD) electrochemical aptasensor is reported for the sensitive determination of tobramycin (TOB). A novel substrate was synthesized by loading cerium-based metal organic framework (Ce-MOF) that was modified by Pd nanoparticles (PdNPs), onto polyethyleneimine (PEI)-modified molybdenum disulfide (MoS2). The substrate (denoted by PEI-MoS2/Ce-MOF@PdNPs) was used to modify the Au electrode (AuE) to expand the electrode surface area for subsequent cDNA loading. Gold-platinum core–shell particles (Au@Pt) loaded with aptamers (Apt) were introduced as signal tags and mimetic peroxidase to hybridize with cDNA and form a double-stranded structure. When the target was present, strand displacement dominated by TISD occurred and the signal tag was released from the electrode surface, turning the signal off. Using the optimal conditions, the linear range of the sensor was from 5 × 10−11 to 1 × 10−6 mol/L and the detection limit was 1.05 × 10−12 mol/L with good stability, reproducibility, and specificity. The aptasensor provided good performance for the determination of tobramycin in milk.

An ultrasensitive electrochemical aptasensor using Tyramide-assisted enzyme multiplication for the detection of Staphylococcus aureus

In this study, we aimed to introduce a new electrochemical aptasensor based on the tyramide signal amplification (TSA) technology for a highly-sensitive detection of the pathogenic bacterium, Staphylococcus aureus, as a model of foodborne pathogens. In this aptasensor, the primary aptamer, SA37, was used to specifically capture bacterial cells; the secondary aptamer, SA81@HRP, was used as the catalytic probe; and a TSA-based signal enhancement system comprising of biotinyl-tyramide and streptavidin-HRP as electrocatalytic signal tags was adopted to fabricate the sensor and improve the detection sensitivity. S. aureus cells were selected as the pathogenic bacteria to verify the analytical performance of this TSA-based signal-enhancement electrochemical aptasensor platform. After the simultaneous binding of SA37-S. aureus-SA81@HRP formed on the gold electrode, thousands of @HRP molecules could be bound onto the biotynyl tyramide (TB) displayed on the bacterial cell surface through a catalytic reaction between HRP and H2O2, resulting in the generation of the highly amplified signals mediated by HRP reactions. This developed aptasensor could detect S. aureus bacterial cells at an ultra-low concentration, with a limit of detection (LOD) of 3 CFU/mL in buffer. Furthermore, this chronoamperometry aptasensor successfully detected target cells in both tap water and beef broth with LOD to be 8 CFU/mL, which are very high sensitivity and specificity. Overall, this electrochemical aptasensor using TSA-based signal-enhancement could be a very useful tool for the ultrasensitive detection of foodborne pathogens in food and water safety and environmental monitoring.

One-Pot Synthesis of Enzyme and Antibody/CaHPO4 Nanoflowers for Magnetic Chemiluminescence Immunoassay of Salmonella enteritidis.

In this study, through a bioinspired strategy, the horseradish peroxidase (HRP) and antibody (Ab) were co-embedded into CaHPO4 to prepare HRP-Ab-CaHPO4 (HAC) bifunctional hybrid nanoflowers by one-pot mild coprecipitation. The as-prepared HAC hybrid nanoflowers then were utilized as the signal tag in a magnetic chemiluminescence immunoassay for application in the detection of Salmonella enteritidis (S. enteritidis). The proposed method exhibited excellent detection performance in the linear range of 10-105 CFU/mL, with the limit of detection (LOD) of 10 CFU/mL. This study indicates great potential in the sensitive detection of foodborne pathogenic bacteria in milk with this new magnetic chemiluminescence biosensing platform.

Iridium (IV) oxide-mediated microorganism nanozyme amplified immunochromatographic assay for dual-signal sensitive detection of salbutamol

Salbutamol (SAL) residues in edible animal tissues have various adverse effects on human health after digestion. Herein, we constructed an innovative functionalized microorganism nanozyme-mediated immunochromatographic assay for sensitive and accurate dual-colorimetric detection of SAL by introducing the Yeast@IrO 2 as bifunctional signal tag. The Yeast@IrO 2 was synthesized by self-assembling iridium (IV) oxide nanoparticles (IrO 2 NPs) on the surface of inactivated yeast cells, which showed high monodispersity, uniform shapes, preeminent biocompatibility and rapid antibodies labeling capacity. After reaction for 15 min, through further employing [3,3′,5,5’ Tetramethylbenzidine (TMB) and hydrogen peroxide (H 2 O 2 )] as substrate to trigger the color reaction, the developed biosensor performed with outstanding performance, including limit of detection (0.012 ng/mL), linearity (R 2 > 0.99) and selectivity. Concurrently, the visual limit of detection (0.2 μg/kg) and satisfactory recoveries (85.6%–103.9%) were obtained by monitoring SAL in pig liver and beef samples. Briefly, this work provided a universal platform for sensitive, precise and rapid detection of toxic and hazardous substances in food safety fields. • A microorganism nanozyme-mediated ICA was developed to detect salbutamol. • The Yeast@IrO 2 was designed by self-assembling IrO 2 NPs on inactivated yeast cells. • The Yeast@IrO 2 generated colorimetric- and catalytic-based dual signals. • The sensor showed lower detection limit (0.012 ng/mL) and broader detection range. • The sensor could be applied to the detection of SAL in beef and pig liver samples.

Highly sensitive homogeneous electrochemiluminescence biosensor for microRNA-155 based on enzyme-free cascade signal amplification and magnetic assisted enrichment

MicroRNA-155 (miR-155) can act as a suitable biomarker for dry eye diseases caused by Sjögren's syndrome. Since the concentration of miR-155 in the clinic samples is low, it is necessary to develop some simple but sensitive detection methods. In this study, a homogeneous electrochemiluminescence (ECL) biosensor for miR-155 detection based on catalyze hairpin assembly (CHA) and hybridization chain reaction (HCR) and magnetic assisted enrichment had been constructed. Firstly, biotin-modified hairpin H1 (bio-H1) had been connected with the streptavidin-modified magnetic beads (SAMBs) to capture target, which can be used to trigger CHA reaction to complete the first signal amplification with the assistance of hairpin H2. Then the stick end of H2 of the CHA production can trigger the HCR reaction of H3 and H4 and generate long double-stranded DNAs (dsDNAs) on the surface of SAMBs to realize the second signal amplification. Ru(phen)32+ can insert into the dsDNAs to produce SAMBs/dsDNA/Ru and act as signal tags, which can be purified by magnetic separation easily, making the background signal significantly reduced. The ECL intensity of the system had a linear relationship with logarithm of miR-155 concentration in the range of 1 fM ∼ 10 nM, with a detection limit as low as 0.63 fM. The proposed biosensor had been applied to monitor miR-155 in clinical samples with satisfied results.

An efficient electrochemical biosensor for the detection of heavy metal lead in food based on magnetic separation strategy and Y-DNA structure.

Herein, an electrochemical biosensor was developed based on a magnetic separation strategy for the sensitive detection of the heavy metal Pb2+. The specific binding of Pb2+ and the aptamer (Apt) is used to trigger the release of the complementary chain (cDNA) on the magnetic bead system. The cDNA completes base complementary pairing with hairpins HP1 and HP2 at the electrode to form a Y-DNA structure. Then, the Y-DNA runs continuously with the assistance of the signal tag methylene blue (MB) and the current signal increases. However, in the absence of Pb2+, cDNA cannot be released and the Y-DNA structure cannot be formed on the electrode, resulting in a relatively low current signal. Under the optimal experimental conditions, the reduced peak current difference (ΔI) showed a good linear relationship with lg CPb2+ between 0.1 and 1000 nM, with a detection limit of 5.9 pM. In addition, the stability, reproducibility and detection capability of the sensors were investigated with satisfactory results.

Aptamer-functionalized two-photon SiO2@GQDs hybrid-based signal amplification strategy for targeted cancer imaging.

Targeted imaging is playing an increasingly important role in the early detection and precise diagnosis of cancer. This need has motivated research into sensory nanomaterials that can be constructed into imaging agents to serve as biosensors. Graphene quantum dots (GQDs) as a valuable nanoprobe show great potential for use in two-photon biological imaging. However, most as-prepared GQDs exhibit a low two-photon absorption cross-section, narrow spectral coverage, and "one-to-one" signal conversion mode, which greatly hamper their wide application in sensitive early-stage cancer detection. Herein, a versatile strategy has been employed to fabricate an aptamer Sgc8c-functionalized hybrid as a proof-of-concept of the signal amplification strategy for targeted cancer imaging. In this study, GQDs with two-photon imaging performance, and silica nanoparticles (SiO2 NPs) as nanocarriers to provide amplified recognition events by high loading of GQD signal tags, were adopted to construct a two-photon hybrid-based signal amplification strategy. Thus, the obtained hybrid (denoted SiO2@GQDs) enabled extremely strong fluorescence with a quantum yield up to 0.49, excellent photostability and biocompatibility, and enhanced bright two-photon fluorescence up to 2.7 times that of bare GQDs (excitation at 760 nm; emission at 512 nm). Moreover, further modification with aptamer Sgc8c showed little disruption to the structure of the SiO2@GQDs-hybrid and the corresponding two-photon emission. Hence, SiO2@GQDs-Sgc8c showed specific responses to target cells. Moreover, it could be used as a signal-amplifying two-photon nanoprobe for targeted cancer imaging with high specificity and great efficiency, which exhibits a distinct green fluorescence compared to that of GQDs-Sgc8c or SiO2@GQDs. This signal amplification strategy holds great potential for the accurate early diagnosis of tumors and offers new tools for the detection a wide variety of analytes in clinical application.

Electrochemical Immunosensor Using Electroactive Carbon Nanohorns for Signal Amplification for the Rapid Detection of Carcinoembryonic Antigen

In this work, a novel sandwich-type electrochemical immunosensor was developed for the quantitative detection of the carcinoembryonic antigen, an important tumor marker in clinical tests. The capture antibodies were immobilized on the surface of a gold disk electrode, while detection antibodies were attached to redox-tagged single-walled carbon nanohorns/thionine/AuNPs. Both types of antibody immobilization were carried out through Au-S bonds using the novel photochemical immobilization technique that ensures control over the orientation of the antibodies. The electroactive SWCNH/Thi/AuNPs nanocomposite worked as a signal tag to carry out both the detection of carcinoembryonic antigen and the amplification of the detection signal. The current response was monitored by differential pulse voltammetry. A clear dependence of the thionine redox peak was observed as a function of the carcinoembryonic antigen concentration. A linear detection range from 0.001-200 ng/mL and a low detection limit of 0.1385 pg/mL were obtained for this immunoassay. The results showed that carbon nanohorns represent a promising matrix for signal amplification in sandwich-type electrochemical immune assays working as a conductive and binding matrix with easy and versatile modification routes to antibody and redox tag immobilization, which possesses great potential for clinical diagnostics of CEA and other biomarkers.

Smartphone-Based Pressure Signal Readout Device Combined with Bidirectional Immunochromatographic Test Strip for Dual-Analyte Detection

Pressure has been a facile signal readout mode for developing point-of-care testing devices due to the attractive features of portability, accessibility, rapidity, and affordability. Herein, a pressure signal readout device was designed by integrating two homemade needle-type piezoresistive transducers, a controller for a thin-film piezoresistive sensor and a smartphone. Meanwhile, a bidirectional immunochromatographic test strip was designed as an immunoreaction platform for dual-analyte detection. Using PdCuPt nanoparticles with catalase-mimic activity as signal tags, the pressure signals triggered by catalyzed aerogenous reaction were monitored by the pressure signal readout device and read on a smartphone with the Bluetooth module. In this proof-of-principle work, imidacloprid and carbendazim were detected as model analytes. The dynamic ranges for quantitating imidacloprid and carbendazim are 20 pg mL-1 to 50 ng mL-1 and 50 pg mL-1 to 50 ng mL-1, respectively. The whole immunoassay process was completed within 16 min. The recovery values for imidacloprid and carbendazim spiked into herbal medicines are 82.0-110.0 and 84.0-116.0%, respectively, verifying its reliability for real sample detection. As the smartphone APP and controller for a thin-film piezoresistive sensor contain 12 signal channels, the system can be easily extended to meet the demand for high-throughput screening.