Hybrid chain reaction-based and Au/Bi4NbO8Cl/In2S3 layer-by-layer assembled dual-mode photoelectrochemical-electrochemical aptasensor for the detection of Salmonella enteritidis.

Salmonella enteritidis (SE) is a food-borne pathogens that can cause acute gastroenteritis. With the increasing social attention to food safety, the detection method of SE has attracted wide attention. In response to the demand for efficient detection methods of SE, this study constructed a novel dual-mode photoelectrochemical-electrochemical (PEC-EC) aptamer-based biosensor. The sensor was constructed using Bi4NbO8Cl/In2S3 heterojunction as the electrode substrate material, the hybridization chain reaction (HCR) and dye sensitization were used as the signal amplification strategies. Bi4NbO8Cl/In2S3 heterojunction could provide an excellent initial photocurrent response for the sensing platform, and the HCR was opened by the end of complementary DNA (cDNA) and generated an ultra-long DNA double-stranded (dsDNA) "super structure" on the surface of the electrode, which could be embedded with a large number of methylene blue (MB) as the bifunctional probes. Thus, dual-mode output was achieved via the PEC and EC activity of MB. Under the optimized conditions, the PEC and EC signal responses of the system were linear to the logarithm of SE concentration in a range from 1.5 × 102 CFU/mL to 1.5 × 107 CFU/mL. The detection limits were found to be 12.9 CFU/mL and 12.3 CFU/mL using the PEC and EC methods, respectively. The constructed dual-mode biosensor exhibited good performance for real sample analysis, and demonstrated great application potential in the field of SE rapid detection. Moreover, this dual-mode detection strategy provided more accurate and reliable results than the single-mode output.

A split organic photophotochemical transistor/vision sensing platform based on MNZ composite and ZIF-67/CuCoO nanospheres for ultra-sensitive detection of CEA.

In this study, a novel organic photophotochemical transistor (OPECT) biosensing platform was proposed for dual-mode detection of CEA. The dual-mode detecting system is achieved benefit from the exceptional photoelectric performance of MIL-53(Fe) -NH2@ZnIn2S4 (MNZ) and the peroxidase enzyme (POD) activity of ZIF-67/Cu0.76Co2.24O4 (ZIF-67/CuCoO). Ab2- ZIF-67/CuCoO probe was immobilized on a 96-well plate by enzyme-linked immunosorbent assay, which accelerated the oxidation of 3,3,5,5-tetramethylbenzidine (TMB) by hydrogen peroxide and thus successfully realized visual detection of CEA. Additionally, in OPECT biosensing mode, the oxidized form of TMB (oxTMB·) serves as a consumptive agents of the electron donor AA, which cause the photocurrent change of MNZ heterojunction, leading to a decrease in the channel current of poly (ethylenedioxythiophene): poly (styrene sulfonate) (PEDOT: PSS) organic transistor. The integration of nanobiocatalysts and the OPECT system demonstrates excellent detection performance for CEA, with a detection limit as low as 3.24 fg mL-1 and expanded their prospective applications for clinical detection of nucleic acids, proteins, and other tumor markers.

CRISPR/Cas12a dual-mode biosensor for Staphylococcus aureus detection via enzyme-free isothermal amplification.

Accurate and reliable detection of Staphylococcus aureus (S. aureus) is essential for preventing infections, particularly in healthcare and food safety contexts. This work presents a novel dual-mode biosensor that integrates the CRISPR/Cas12a system with an enzyme-free isothermal amplification method for detecting S. aureus. Hybridization chain reaction (HCR) and catalytic hairpin assembly (CHA) amplify the aptamer-triggered response, significantly enhancing sensitivity. CRISPR/Cas12a's nuclease activity is utilized in two modes: cis cleavage generates a fluorescence signal, while trans cleavage produces an electrochemical signal, enabling dual-mode detection. The biosensor demonstrates outstanding performance, with a limit of detection (LOD) as low as 5.7 CFU mL-1 in electrochemical mode and 133.7 CFU mL-1 in fluorescence mode, showcasing excellent accuracy, stability, and sensitivity. It has been successfully applied to detecting actual samples, confirming its practical applicability. This innovative approach offers a powerful tool for the swift and precise identification of S. aureus and paves the way for developing next-generation dual-mode biosensors for various analytes. Future research will aim to simplify the detection process further, making it more accessible for use in resource-limited settings.

CRISPR/Cas12a-drived electrochemiluminescence and fluorescence dual-mode magnetic biosensor for sensitive detection of Pseudomonas aeruginosa based on iridium(III) complex as luminophore.

The opportunistic human pathogen Pseudomonas aeruginosa (P. aeruginosa) poses a significant threat to human health, causing sepsis, inflammation, and pneumonia, so it is crucial to devise an expeditious detection platform for the P. aeruginosa. In this work, bis (2- (3, 5- dimethylphenyl) quinoline- C2, N') (acetylacetonato) iridium (III) Ir (dmpq)2 (acac) with excellent electrochemiluminescence (ECL) and fluorescence (FL) and magnetic nanoparticles were encapsulated in silica spheres. The luminescent units exhibited equal ECL and FL properties compared with single iridium complexes, and enabled rapid separation, which was of vital significance for the establishment of biosensors with effective detection. In addition, the luminescent units were further reacted with the DNA with quenching units to obtain the signal units, and the ECL/FL dual-mode biosensor was employed with the CRISPR/Cas12a system to further improve its specific recognition ability. The ECL detection linear range of as-proposed biosensor in this work was 100 fM-10 nM with the detection limit of 73 fM (S/N = 3), and FL detection linear range was 1 pM-10 nM with the detection limit of 0.126 pM (S/N = 3). Importantly, the proposed dual-mode biosensor exhibited excellent repeatability and stability in the detection of P. aeruginosa in real samples, underscoring its potential as an alternative strategy for infection prevention and safeguarding public health and safety in the future.

Advances in Aptamer-Based Biosensors for the Detection of Foodborne Mycotoxins.

Foodborne mycotoxins (FBMTs) are toxins produced by food itself or during processing and transportation that pose an enormous threat to public health security. However, traditional instrumental and chemical methods for detecting toxins have shortcomings, such as high operational difficulty, time consumption, and high cost, that limit their large-scale applications. In recent years, aptamer-based biosensors have become a new tool for food safety risk assessment and monitoring due to their high affinity, good specificity, and fast response. In this review, we focus on the progress of single-mode and dual-mode aptasensors in basic research and device applications over recent years. Furthermore, we also point out some problems in the current detection strategies, with the aim of stimulating future toxin detection systems for a transition toward ease of operation and rapid detection.

Synergistic powering of DNA walker movement by endogenous dual enzymes for constructing dual-mode biosensors.

To achieve highly sensitive and reliable detection of apurinic/apyrimidinic endonuclease 1 (APE1), a critical cancer diagnostic biomarker, we designed a DNA walker-based dual-mode biosensor, utilizing cellular endogenous dual enzymes (APE 1 and Flap endonuclease 1 (FEN 1)) to collaborate in activating and propelling DNA walker motion on DNA-functionalized Au nanoparticles. Incorporating both fluorescence and electrochemical detection modes, this system leverages signal amplification from DNA walker movement and cascade amplification through tandem hybridization chain reactions (HCR), achieving highly sensitive detection of APE 1. In the fluorescence mode, continuous DNA walker movement, initiated by APE1 and driven by FEN1, generates a robust signal response within a concentration range of 0.01-500 U mL-1, presenting a good linearity in the concentration range of 0.01-10 U mL-1, with a detection limit of 0.01 U mL-1. In the electrochemical detection module, the cascade upstream DNA walker and downstream HCR dual signal amplification strategy further enhances the sensitivity of APE1 detection, extending the linear range to 0.01-50 U mL-1 and reducing the detection limit to 0.002 U mL-1. Rigorous validation demonstrates the biosensor's specificity and anti-interference capability against multiple enzymes. Moreover, it effectively distinguishes cancer cells from normal cell lysates, exhibiting excellent stability and consistency in the dual-modes. Overall, our findings underscore the efficacy of the developed dual-mode biosensor for detecting APE1 in serum and cell lysates samples, indicating its potential for clinical applications in disease diagnosis.

A colorimetric/electrochemical microfluidic biosensor using target-triggered DNA hydrogels for organophosphorus detection.

Organophosphorus compounds are widely distributed and highly toxic to the environment and living organisms. The current detection of organophosphorus compounds is based on a single-mode method, which makes it challenging to achieve good portability, accuracy, and sensitivity simultaneously. This study designed a multifunctional microfluidic chip to develop a dual-mode biosensor employing a DNA hydrogel as a carrier and aptamers as recognition probes for the colorimetric/electrochemical detection of malathion, an organophosphorus compound. The biosensor balanced portability and stability by combining a microfluidic chip and target-triggered DNA hydrogel-sensing technologies. Moreover, the biosensor based on target-triggered DNA hydrogel modified microfluidic developed in this study exhibited a dual-mode response to malathion, providing both colorimetric and electrochemical signals. The colorimetric mode enables rapid visualization and qualitative detection and, when combined with a smartphone, allows on-site quantitative analysis with a detection limit of 56 nM. The electrochemical mode offers a broad linear range (0.01-3000 µM) and high sensitivity (a limit of detection of 5 nM). The two modes could validate each other and improve the accuracy of detection. The colorimetric/electrochemical dual-mode biosensor based on target-triggered DNA hydrogel modified microfluidic chip offers a portable, simple, accurate, and sensitive strategy for detecting harmful environmental and food substances.

Dual-mode biosensor using Tb-Cu MOF@Au nanoenzyme to effectively quench the photocurrent of Bi2O3/Bi2S3/AgBiS2 heterojunction and emit fluorescence for neuron-specific enolases detection.

A novel dual-mode biosensor was constructed for the ultrasensitive detection of neuron-specific enolase (NSE), utilizing Tb-Cu MOF@Au nanozyme as the signal label to effectively quench the photoelectrochemical (PEC) signals of Bi2O3/Bi2S3/AgBiS2 composites and initiate fluorescent (FL) signals. First, Bi2O3/Bi2S3/AgBiS2 heterojunction with excellent photoelectric activity was selected as the substrate material to provide a stable photocurrent. The well-matched energy levels significantly enhanced the separation and transfer of photogenerated carriers. Second, a strategy of consuming ascorbic acid (AA) by Tb-Cu MOF@Au nanozyme was introduced to improve the sensitivity of the PEC/FL biosensor. Tb-Cu MOF@Au not only could catalyze the oxidation of AA, but the steric effect further reduced the contact of AA with the substrate. More importantly, in the presence of H2O2, a significant fluorescence was produced from Tb3+ sensitized by the oxidation products of AA. Based on the above strategies, a highly stable and sensitive dual-mode biosensor was proposed for accurate NSE determination. Third, the developed dual-mode biosensor demonstrated excellent performance in detecting NSE. In this study, the PEC method demonstrated a wide detection range from 0.00005 to 200 ng/mL with a low detection limit of 20 fg/mL. The FL method exhibited a linear range from 0.001 to 200 ng/mL with a detection limit of 0.65 pg/mL. The designed biosensor showed potential practical implications in the accurate detection of disease markers.

Dual-Mode Virus Detection: Combining Electrochemical and Fluorescence Modalities for Enhanced Sensitivity and Reliability.

This study introduces a dual-mode biosensor specifically designed for the quantitative detection of viruses in rapid analysis. The biosensor is unique in its use of both optical (fluorescence) and electrochemical (impedance) detection methods using the same nanocomposites, providing a dual confirmation system for virus (norovirus-like particles) quantification. The system is based on using two antibody-conjugated nanocomposites: CdSeS quantum dots and Au-N,S-GQD nanocomposites. For optical detection, the principle relies on the fluorescence quenching of CdSeS by Au-N,S-GQD in a sandwich structure with the target. Conversely, electrochemical detection is based on the change in impedance caused by the formation of the same sandwich structure. The biosensor demonstrated exceptional sensitivity, capable of detecting norovirus at concentrations of as low as femtomolar in the electrochemical method and picomolar in the optical method. In the dual-responsive concentration range from 10-13 to 10-10 M, the sensor is highly sensitive in both methods, creating significant changes in fluorescence intensity and impedance in the presence of virus. Furthermore, the biosensor exhibits a high degree of specificity, with a negligible response to nontarget proteins, even within complex test solutions. This work represents a significant advancement in the field of biosensor technology, offering a fast, accurate, and reliable method for diagnosing viral infections and diseases.

Ultrathin-FeOOH-coated MnO2 nanozyme with enhanced catalase-like and oxidase-like activities for photoelectrochemical and colorimetric detection of organophosphorus pesticides.

Herein, we develop a dual-mode biosensor for photoelectrochemical and colorimetric detection of organophosphate pesticides (OPPs) based on ultrathin-FeOOH-coated MnO2 (MO@FHO) nanozyme. In this biosensor, OPPs can inhibit the alkaline phosphatase (ALP) activity and hinder the dephosphorylation of l-ascorbic acid-2-phosphate, preventing the decomposition of MO@FHO nanozyme and inducing both a photoelectrochemical (PEC) signal and the colorimetric change. The MO@FHO nanozyme not only possesses an enhanced catalase-like activity to degrade H2O2 for the generation of an improved cathodic photocurrent, but also exhibits an excellent oxidase-like activity to oxidize 3,3,5,5-tetramethylbenzidine with high catalytic efficiency. This biosensor displays a detection limit of 50 pmol/L for the PEC mode and a detection limit of 0.8 nmol/L for the colorimetric mode. Moreover, this biosensor exhibits excellent performance in complex biological matrices, and the smartphone-based visual sensing platform facilitates rapid and sensitive detection of OPPs, holding promising applications in food safety monitoring, and on-site detection.

Fluorophore and nanozyme-functionalized DNA walking: A dual-mode DNA logic biocomputing platform for microRNA sensing in clinical samples.

Inspired by the programmability and modifiability of nucleic acids, point-of-care (POC) diagnostics for nucleic acid target detection is evolving to become more diversified and intelligent. In this study, we introduce a fluorescent and photothermal dual-mode logic biosensing platform that integrates catalytic hairpin assembly (CHA), toehold-mediated stand displacement reaction (SDR) and a DNA walking machine. Dual identification and signal reporting modules are incorporated into DNA circuits, orchestrated by an AND Boolean logic gate operator and magnetic beads (MBs). In the presence of bispecific microRNAs (miRNAs), the AND logic gate activates, driving the DNA walking machine, and facilitating the collection of hairpin DNA stands modified with FAM fluorescent group and CeO2@Au nanoparticles. The CeO2@Au nanoparticles, served as a nanozyme, can oxidize TMB into oxidation TMB (TMBox), enabling a near-infrared (NIR) laser-driven photothermal effect following the magnetic separation of MBs. This versatile platform was employed to differentiate between plasma samples from breast cancer patients, lung cancer patients, and healthy donors. The thermometer-readout transducers, derived from the CeO2@Au@DNA complexes, provided reliable results, further corroborated by fluorescence assays, enhancing the confidence in the diagnostics compared to singular detection method. The dual-mode logic biosensor can be easily customized to various nucleic acid biomarkers and other POC signal readout modalities by adjusting recognition sequences and modification strategies, heralding a promising future in the development of intelligent, flexible diagnostics for POC testing.

SPRi/SERS dual-mode biosensor based on ployA-DNA/ miRNA/AuNPs-enhanced probe sandwich structure for the detection of multiple miRNA biomarkers.

MicroRNA (miRNA) has broad application prospects in the early detection of various cancers. In this work, a SPRi/SERS dual-mode biosensor was developed on the same gold chip by AuNPs as the reinforcing medium. High throughput and sensitivity detection of three typical cervical cancer markers miRNA21, miRNA124 and miRNA143 were achieved based on the sandwich structure of polyA blocks-DNA capture probe/target miRNA/AuNPs-assistant probe or SERS nanoprobes. AuNPs greatly improved the SPR response due to mass increase and more sensitive refractive index changes. Meanwhile, due to the LSPR effect of AuNPs, the signal of SERS nanoprobe can be amplified. The miRNAs were detected in serum to verify its practicality. SPRi achieved detection of three miRNAs simultaneously. LODs were 6.3 fM, 5.3 fM and 4.6 fM, respectively, and wide dynamic response range of 500 pM-10 nM. While SERS assay ensured high sensitivity with LODs as low as 1 fM, 0.8 fM and 1.2 fM, respectively, and with the recoveries in the range of 90.0 %-100.2 %. The redundant detection signals of the two modes can provide more reliable data to prevent false positive or false negative detection, and have great application prospects in detection of cancer-related nucleic acids in early stage of disease.

NIR-driven photoelectrochemical-fluorescent dual-mode biosensor based on bipedal DNA walker for ultrasensitive detection of microRNA.

Optical biosensors have become powerful tools for bioanalysis, but most of them are limited by optic damage, autofluorescence, as well as poor penetration ability of ultraviolet (UV) and visible (Vis) light. Herein, a near-infrared light (NIR)-driven photoelectrochemical (PEC)-fluorescence (FL) dual-mode biosensor has been proposed for ultrasensitive detection of microRNA (miRNA) based on bipedal DNA walker with cascade amplification. Fueled by toehold-mediated strand displacement (TMSD), the bipedal DNA walker triggered by target miRNA-21 is formed through catalytic hairpin assembly (CHA), which can efficiently move along DNA tracks on CdS nanoparticles (CdS NPs)-modified fluorine doped tin oxide (FTO) electrode, resulting in the introduction of upconversion nanoparticles (UCNPs) on electrode surface. Under 980 nm laser irradiation, the UCNPs serve as the energy donor to emit UV/Vis light and excite CdS NPs to generate photocurrent for PEC detection, while the upconversion luminescence (UCL) at 803 nm is monitored for FL detection. This PEC-FL dual-mode biosensor has achieved the ultrasensitive and accurate analysis of miRNA-21 in human serum and different gynecological cancer cells. Overall, the proposed dual-mode biosensor can not only couple the inherent features of each single-mode biosensor but also provide mutual authentication of testing results, which opens up a new avenue for early diagnosis of miRNA-related diseases in clinic.

Proximity hybridization regulated dual-mode ratiometric biosensor for estriol detection in pregnancy serum.

Sensitive and accurate determination of estriol level is vastly significant for the fetal growth and development. Herein, we constructed a dual-mode ratiometric biosensor for estriol assay combining the competitive immunoreaction, proximity hybridization with a two-step resonance energy transfer (RET) strategy. Estriol antibody and goat anti-rabbit antibody labeled DNA probes (Ab1-DNA1-Pt NPs and Ab2-DNA2) both hybridized with silver nanoclusters labeled DNA strands (H1-Ag NCs). Thus, the formed proximity hybridization enabled the occurrence of fluorescence RET (FL-RET, as the primary RET) between Ag NCs (donor) and Pt NPs (acceptor), quenching FL intensity of Ag NCs (FL off). When target estriol existed, the competitive reaction of Ab1-DNA1-Pt NPs with estriol and Ab2-DNA2 avoided the proximity hybridization. Then, the estriol-dependent H1-Ag NCs quenched electrochemiluminescence (ECL) emission of CdS quantum dots (CdS QDs, ECL off), generating ECL-RET (as the second RET). Consequently, according to the reverse changes of FL and ECL responses, this sensor realized the quantification of estriol from 1 to 100 ng/mL. Moreover, satisfactory results were achieved while testing estriol in pregnancy serum specimens, suggesting that the system is promising for potential application in samples analysis.

Sensitive dual-mode sensing platform for Amyloid ß detection: Combining dual Z-scheme heterojunction enhanced photoelectrochemistry analysis and dual-wavelength ratiometric electrochemiluminescence strategy.

As a tumor biomarker, the accumulation of amyloid ß oligomers (Aßo) in the brain has been suggested as a key feature in the pathogenesis and progression of Alzheimer's disease (AD). In this work, we designed a novel photoelectrochemical (PEC) and electrochemiluminescence resonance energy transfer (ECL-RET) dual-mode biosensor to achieve ultra-sensitive detection of Aßo. Specifically, the electrode surface modified Carbon Dots (C Dots) and the electrodeposited polyaniline (PANI) film formed a Z-scheme heterojunction reversing the photocurrent signal, and then the Aßo specific recognition peptide was attached to the surface via amide bonding between the amino group of PANI and carbonyl group of peptide. After that, in the presence of CdTe labeled specific recognition aptamer for Aß (CdTe-Apt), Aßo was captured to construct a sandwich-type biosensor and exhibited a significantly enhanced cathodic photocurrent response because the formed dual Z-scheme heterojunction promoted charge separation efficiency. Interestingly, the proposed biosensor also caused a ratiometric change in the ECL intensity at 555 nm and 640 nm. Therefore, the developed biosensor achieved dual-mode detection of Aßo, where the PEC detection range of Aßo was from 10 fM to 0.1 µM (with a detection limit of 4.27 fM) and the ECL method provided a linear detection range of 10 fM to 10 nM (with a detection limit of 6.41 fM). The stability and reliability of the experimental results indicate that this has been a promising biosensing pattern and could be extended to the analysis of other biomarkers.

A convenient fluorescent/electrochemical dual-mode biosensor for accurate detection of Pb2+ based on DNAzyme cycle.

The presence of heavy metals in the ecological environment is a serious threat to human health. Therefore, it is very important to establish a simple and sensitive method for the detection of heavy metals. Currently, most of the methods are single-channel sensing, and these methods are prone to false-positive signals, which reduces the accuracy. In this work, Pb2+-DNAzyme was immobilized on magnetic beads (MBs) using a linkage of biotin and streptavidin and successfully applied to the construction of a fluorescent/electrochemical dual-mode (DM) biosensor. The supernatant after magnetic separation formed a double strand on the electrode, which was combined with methylene blue (MB) for electrochemical detection (EC). At the same time, FAM-d was added to the precipitate, and after magnetic separation, the supernatant was subjected to fluorescent detection (FL). Under optimal conditions, the signal response of the constructed dual-mode biosensor showed a good linear relationship with the concentration of Pb2+. The DNAzyme-based dual-mode biosensor achieved sensitive and selective detection of Pb2+ with good accuracy and reliability, opening a new way for the development of biosensing strategies for the detection of Pb2+. More importantly, the sensor has high sensitivity and accuracy for the detection of Pb2+ in actual sample analysis.

A colorimetric and photothermal dual-mode biosensing platform based on nanozyme-functionalized flower-like DNA structures for tumor-derived exosome detection.

Tumor-derived exosomes can be served as a kind of promising biomarkers for early diagnosis of cancers. Herein, a colorimetric/photothermal dual-mode exosomes sensing platform is developed for human breast cancer cell (MCF-7)-derived exosomes based on encapsulation of 3,3',5,5'-tetramethylbenzidine-loaded graphene quantum dot nanozymes (TMB-GQDzymes) into DNA flowers (DFs) via rolling circle amplification (RCA). To achieve specific detection, EpCAM aptamer for MCF-7 cell-derived exosomes is immobilized on the well plate, while the complementary sequence of another CD63 aptamer is designed into the circular template to obtain abundant capture probes. Benefitting from the dual-aptamer recognition strategy, a sandwich structure of EpCAM aptamer/exosomes/TMB-GQDzymes@DFs is formed, in which the GQDzymes can catalyze the oxidation of TMB in the presence of H2O2. The resulting products of TMB oxidation (oxTMB) can induce not only the absorption changes but also a near-infrared (NIR) laser-driven photothermal effect, achieving dual-mode detection of exosomes with the limit of detection (LOD) of 1027 particles/µL (colorimetry) and 2170 particles/µL (photothermal detection), respectively. In addition, this sensing platform has demonstrated excellent performance to well distinguish breast cancer patients from healthy individuals in serum samples analysis. Overall, the proposed dual-readout biosensor opens promising prospects for exosome detection in biological study and clinical applications.

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.

Magnetic relaxation switch and fluorescence dual-mode biosensor for rapid and sensitive detection of ricin B toxin in edible oil and tap water.

The ultrasensitive and rapid detection of ricin B toxin (RTB) is essential for food safety and environmental monitoring. Herein, a dual-mode magnetic relaxation switch (MRS) and fluorescence (FL) biosensing strategy was developed to efficiently detect RTB using fluorescent magnetic nanoparticles (MNP300@SiO2(FITC)). Meanwhile, the as-prepared composite MNP300@SiO2(FITC) exhibited superior biocompatibility and increased FL readout and was coupled with aptamer (Apt) to form a captured probe. Magnetic nanoparticles, 30 nm in diameter (MNP30), were coupled to a Blocker to form a paired probe to compete with RTB for Apt binding. The presence of the RTB triggered the dual-mode detection switch, thus, weakening the magnetic and fluorescent signals. Compared with the single-mode detection method, the Δ T2 and Δ FL intensity here exhibited an excellent linear relationship with logarithm of RTB concentrations at 0.001-500 ng/mL and 0.005-500 ng/mL, and obtained ultrahigh sensitivities of 0.8 pg/mL and 3 pg/mL, respectively. In addition, the dual-mode biosensor gained satisfactory spiked recoveries and relative standard deviations for quantitative detection of spiked RTB in edible oil and tap water samples. To our knowledge, this is the first study to describe the accurate quantification of RTB using a sensitive MRS-FL biosensor. We anticipate that this strategy will provide novel avenues for the development of dual-mode sensing assays.

A gold nanoparticle-dye/poly(3-aminobenzylamine)/two dimensional MoSe2/graphene oxide electrode towards label-free electrochemical biosensor for simultaneous dual-mode detection of cancer antigen 15-3 and microRNA-21.

A dual-mode electrochemical biosensor is successfully developed for simultaneous detection of two different kinds of breast cancer biomarkers, namely cancer antigen 15-3 (CA 15-3) and microRNA-21 (miRNA-21), for the first time. The sensor composes of a poly(3-aminobenzylamine)/two-dimensional (2D) molybdenum selenide/graphene oxide nanocomposite modified two-screen-printed carbon electrode array (dual electrode), functionalized individually with 2,3-diaminophenazine-gold nanoparticles and toluidine blue-gold nanoparticles. Both kinds of the redox probe-gold nanoparticles are employed as signaling molecules and supports for immobilization of anti-CA 15-3 antibodies and capture DNA-21 probes, respectively. Due to the good conductivity and high surface-to-volume ratio of the nanocomposite, high amount of the antibodies and capture probes can be immobilized on the modified dual-electrode, giving the efficient duplex detection. Consequently, the biosensor provides good selectivity, and high sensitivity for the dual target analyte detection. The experimental results show that this label-free biosensor exhibits good linear responses to the concentrations of both target analytes with the limits of detection (LODs) of 0.14 U mL-1 and 1.2 fM for CA 15-3 and miRNA-21, respectively. This assay strategy has a great potential to be further developed for the simultaneous detection of a variety of miRNAs and protein biomarkers for point-of-care (POC) diagnostic applications.