Dual-mode Detection Research Articles

Smartphone-assisted portable swabs for blood glucose management: A point-of-use assay for dual-mode visual detection based on bifunctional carbon dots

Controlling glucose (Glu) intake is a “required course” for diabetics, thus quickly and precisely measuring the amount of Glu in food is crucial. For this purpose, a novel smartphone-assisted portable swab for the dual-mode visual detection of Glu was constructed combined the selectivity of natural enzymes with the controllable catalytic activity of nanozymes. Glu was specifically decomposed by glucose oxidase (natural enzyme) to produce H2O2, which was catalyzed by carbon dots (FeMn/N-CDs, nanozyme) to accelerate the reaction of o-phenylenediamine (OPD, colorless) to produce 2,3-diaminophenazine (DAP, yellow). As a result, the absorbance at 450 nm gradually increased with the increasing concentration of Glu, leading to a color change in the system from colorless to yellow. Meanwhile, the fluorescence of FeMn/N-CDs gradually decreased at 450 nm, while the fluorescence of DAP gradually increased at 550 nm, allowing for both ratiometric fluorescence and colorimetric dual-mode detection. Furthermore, natural enzyme and nanozyme together with OPD were co-loaded on the swabs to achieve cascade catalysis of Glu. The assembled portable swabs have detection ranges of 1–600 μM (LOD = 0.37 μM) and 4–1200 μM (LOD = 1.19 μM) for the colorimetric and fluorometric detection, respectively. The field test results on real samples demonstrated that the portable swabs have great promise for use in efficiently and accurately guiding the dietary intake of diabetics.

Platinum nanoparticle oxidase-like enzyme for colorimetric and photothermal dual-mode detection of sulfide ions

Monitoring sulfide ions (S2-) in environmental matrices is critical for environmental safety and pollution control. In this work, a novel dual-mode colorimetric and photothermal (PT) point-of-care testing (POCT) platform was developed for S2- assay. The synthesized platinum nanoparticles (Pt NPs) exhibited exceptional oxidase-like activity, catalyzing the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) to its oxidized form (oxTMB), causing a color change from colorless to blue. Additionally, oxTMB exhibits significant PT effects under near-infrared 808 nm laser irradiation. The presence of S2- induced the aggregation of Pt NPs, markedly inhibiting their oxidase-like activity, thereby establishing an inverse relationship between the concentration of S2- and both the RGB value and temperature change in TMB solution. The limits of detection (LODs) were calculated to be 1.5 μM and 4.4 μM for colorimetric and photothermal analysis using a digital thermometer and smartphone, respectively. The S2- in lake water and fuel residue was analyzed, yielding satisfactory results. This method offers low-cost, straightforward, and swift advantages, underscoring its potential for POCT in environmental monitoring.

Precision detection of cyanide, fluoride, and hydroxide ions using a new tetraseleno-BODIPY fluorescent sensor

A new chemosensor based on Seleno-BODIPY (4) was designed and synthesized for the rapid and sensitive detection of CN–, F−, and OH– ions in THF, exhibiting ultra-low detection limits of 26.26 nM, 43.05 nM, and 8.64 nM, respectively, through a turn-on fluorescent process. The seleno-funcionalization step was based on a novel methodology developed by our group, allowing direct functionalization of the BODIPY core. This procedure involves a quick reaction utilizing Ph2Se2 as a selenium source, BPO (benzoyl peroxide), and p-TSA (p-toluenesulfonic acid) in acetonitrile, enabling the production of the corresponding chalcogenated BODIPYs containing one to four selenium groups, demonstrating its versatility. The structure of BODIPY 4 was confirmed by HRMS, 1H, 13C, 77Se NMR, and IR spectra, and its photophysical properties were also evaluated. BODIPY 4 was applied to detect CN–, F−, and OH– ions in dual-mode detection (UV–Vis and fluorescence spectra), displaying a ratiometric response. The new probe exhibited a fast response time, visual color change from blue to fluorescent yellow, and high sensitivity and selectivity for these analytes over other selected anions. Mechanistic investigation through mass analysis revealed that the detection of these anions by BODIPY 4 occurs via an Aromatic Nucleophilic Substitution reaction with phenylselenide as the leaving group.

Dual-mode SERS-ECL biosensor for robust detection of circulating miRNAs based on in-situ synthesized probes

A novel dual-mode biosensor integrating surface-enhanced Raman spectroscopy (SERS) and electrochemiluminescence (ECL) was developed for the reliable detection of acute myocardial infarction (AMI) related circulating miRNAs. The DNA walker nucleic acid amplification technique was employed for signal amplification and facilitated in-situ synthesis of ECL luminescent clusters and SERS probes. The alkynyl-modified silver nanocluster (AgNC) template strand and the azido-modified DNA probe on the electrode were connected through linker release facilitated by the continuous rolling and cutting action of the DNA walker on the spherical substrate. Under Cu+ catalysis, the alkynyl and azide groups at the junction undergo conversion into triazole molecules, which can serve as SERS probes. Subsequently, AgNCs were synthesized using a template method, with SERS signals emitted due to plasma resonance effects of triazole molecules situated between Au nanoparticles and AgNCs. The developed dual-mode analysis platform efficiently minimizes the potential for signal leakage, significantly corrects systematic errors, improves detection accuracy and sensitivity, and facilitates dependable identification of circulating miRNA. The detection of miRNA-133a exhibited a linear relationship within the concentration range of 100 aM to 1 nM, with detection limits of 32 aM and 0.17 fM in ECL and SERS modes, respectively. The SERS-ECL dual-mode detection platform may provide forward-looking ideas for the field of biosensing and clinical analysis.

Precise counter anion modulation of the self-assembly behavior-endowed ultrasensitive and specific dual-mode visualization of nitrate

Pt(II) polypyridine complex-based probe exhibits promising performance in anion detection by the change of the absorption and emission properties based on supramolecular self-assembly. However, whether one can develop a modulation strategy of the counter anion to boost the detection sensitivity and anti-interference capability of the Pt(II) complex-based probe remains a big challenge. Here, an effective modulation strategy was proposed by precisely regulating the interaction energy through adjusting the type of the counter anions, and a series of probes have been synthesized by counter anion (X = Cl-, ClO4-, PF6-) exchange in [Pt(tpy)Cl]·X (tpy=2,2′:6′,2′’-terpyridine), and thus the colorimetric-luminescence dual-mode detection toward nitrate was achieved. The optimal [Pt(tpy)Cl]·Cl probe shows superior nitrate detection performance including a limit of detection (LOD) (8.68 nM), rapid response (<0.5 s), an excellent selectivity and anti-interference capability even facing 14 common anions. Moreover, a polyvinyl alcohol (PVA) sponge-based sensing chip loaded with the probe enables the ultra-sensitive detection of nitrate particles with an ultralow detection limit of 7.6 pg, and it was further integrated into a detection pen for the accurate recognition of nitrate particles in real scenarios. The proposed counter-anion modulation strategy is expected to start a new frontier for the exploration of novel Pt(II) complex-based probes.

A novel electropolymerized molecularly imprinted dual-mode sensor for bisphenol AF detection in pond mud

Recently, bisphenol AF (BPAF) as most commonly used bisphenol A analogs had the increasing higher level in the environment with unknown risks. Herein, a synchronous dual-mode sensor had been established based on differential pulse voltammetry (DPV) and electrochemiluminescence (ECL) for the detection of BPAF in pond mud. Firstly, the sensing molecularly imprinted polymer (MIP) films were prepared by electrochemical polymerization procedure with 3,4-ethoxylene dioxy thiophene (EDOT) as the functional monomer, BPAF as the template molecule and MXene as the supporting electrolyte. Due to unique characters of PEDOT and MXene, the constructed MIP films were stable and highly conductive. Meanwhile, zinc-doped bismuth sulfide quantum dots (Zn-Bi2S3 QDs) were synthesized as a nano-emitter to generate strong ECL signals in the MIP film. In the sensing process, a pulsed voltage applied to the PEDOT/MXene MIP film to generate both DPV and ECL signals for simultaneous dual-mode detection. Additionally, the liquid-liquid extraction with deep eutectic solvent (menthol: octanol 1:1) was used for the pre-concentration of the BPAF in the pond mud. Based on the sensing system, the ECL and DPV response showed the good linear relationships with the concentration of BPAF with the ranges of 0.01 μM–50 μM and 0.1 μM–50 μM and the detection limits of 0.0060 μM and 0.059 μM, respectively.

B, N co-doped carbon dots as efficient nanozymes for colorimetric and fluorometric dual-mode detection of cholesterol

In this work, the B, N co-doped carbon dots (B, N-CDs) were synthesized via facile hydrothermal approach with 6-aminopyridine boronic acid as precursor. In addition to emitting intense blue luminescence when exposed to ultraviolet light, the prepared B, N-CDs displayed remarkable peroxidase-like activity, which could efficiently catalyze the oxidation of 3, 3′, 5, 5′ -tetramethylbenzidine (TMB) to blue ox-TMB in the presence of hydrogen peroxide (H2O2). Furthermore, the fluorescence intensity of B, N-CDs increased gradually upon the addition of H2O2. Since cholesterol oxidase (ChOx) can catalyze the oxidation of cholesterol to form H2O2, the as-prepared B, N-CDs was then used as both colorimetric and fluorometric sensors for the detection of cholesterol with detection limit of 0.87 and 2.31 μM, respectively. Finally, the dual-mode approach based on B, N-CDs was effectively utilized for detecting cholesterol levels in serum samples, proving the potential application of B, N-CDs in the field of biological assay.

Self-designed portable dual-mode fluorescence device with custom python-based analysis software for rapid detection via dual-color FRET aptasensor with IoT capabilities

An innovative aptasensor incorporating MoS2-modified bicolor quantum dots and a portable spectrometer, designed for the simultaneous detection of ochratoxin A (OTA) and aflatoxin B1 (AFB1) in corn was developed. Carbon dots and CdZnTe quantum dots were as nano-donors to label OTA and AFB1 aptamers, respectively. These labeled aptamers were subsequently attached to MoS2 receptors, enabling fluorescence resonance energy transfer (FRET). With targets, the labeled aptamers detached from the nano-donors, thereby disrupting the FRET process and resulting in fluorescence recovery. Furthermore, a portable dual-mode fluorescence detection system, complemented with customized python-based analysis software, was developed to facilitate rapid and convenient detection using this dual-color FRET aptasensor. The developed host program is connected to the spectrometer and transmits data to the cloud, enabling the device to have Internet of Things (IoT) characteristics. Connected to the cloud, this IoT-enabled device offers convenient and reliable fungal toxin detection for food safety.

Carbon Quantum Dots (CQDs)-Diphenyl Carbazone (DPCO) loaded thin film sensors for fluorescent and colorimetric dual mode detection of mercury in various water resources

Mitigation of the environmental pollution has attracted huge attention in recent years owing to the caused health hazards. Mercury ions are one of the toxic heavy metals as pollutants that cause severe damage to health and the environment. Fluorometric and colorimetric-based detection of mercury in water resources is gaining popularity globally due to ease of measurement and the possibility of onsite measurement. We herein report a fluorescent and colorimetric dual-mode Diphenyl carbazone (DPCO) and Carbon quantum dots (CQDs) thin film sensor for specific detection of mercury ions. The thin film sensors were characterized using various techniques like XPS, XRD, TEM, and CLSM. The colorimetric detection is based on the specific binding of DPCO with mercury ions forming a violet-colored complex with simultaneous production of protons. The intensity of color formation was quantified with a smartphone camera and the images using ImageJ software yielding a limit of detection (LOD) of 290 ppb. Fluorometric estimation was performed at an excitation wavelength of 365 nm and an emission wavelength of 505 nm which was possible due to the pH sensitive nature of CQDs in the thin film. Mercury (Hg2+) detection to an extent of 1.8 ppb was made possible in the linear range of 0–100 μM using fluorometric method with a response time of 2 min. Accuracy of estimation of Hg2+ detection was evaluated by spiking different water samples like Tap water, and two river water samples and resulted in the range of 100–103 %. Current investigation shows that DPCO-CQDs loaded thin films coupled with a fiber-optic device and smartphone imaging could be used for accurate dual mode sensing of Hg2+ in real water resource samples.

Rapidly and simply detecting Cr (VI) in aqueous media via a diketopyrrolopyrrole-based chemosensor with both high selectivity and low LOD

BackgroundThe high toxicity of hexavalent chromium [Cr (VI)] could not only cause harmful effects on humans, including carcinogenicity, respiratory issues, genetic damage, and skin irritation, but also contaminate drinking water sources, aquatic ecosystems, and soil, impairing the reproductive capacity, growth, and survival of organisms. Due to these harmful effects, detecting toxic Cr (VI) is of great significance. However, the rapid, simple, and efficient detection at a low Cr (VI) concentration is extremely challenging, especially in an acidic condition (existing as HCrO4−) due to its low adsorption free energy. ResultsA diketopyrrolopyrrole-based small molecule (DPPT-PhSMe) is designed and characterized to act as a chemosensor, which allows a high selectivity to Cr (VI) at an acidic condition with a low limit of detection to 10−8 M that is two orders of magnitude lower than the cut of limit (1 μM) recommended by World Health Organization (WHO). Mechanism study indicates that the rich sulfur atoms enhance the affinity to HCrO4−. Combining with favorable features of diketopyrrolopyrrole, DPPT-PhSMe not only allows dual-mode detection (colorimetric and spectroscopic) to Cr (VI), but also enables disposable paper-based sensor for naked-eye detection to Cr (VI) from fully aqueous media. The investigation of DPPT-PhSMe chemosensor for the quantification of Cr (VI) in real life samples demonstrates a high reliability and accuracy with an average percentage recovery of 102.1 % ± 4 (n = 3). SignificanceDPPT-PhSMe represents the first diketopyrrolopyrrole-derived chemosensor for efficient detection to toxic Cr (VI), not only providing a targeted solution to the bottleneck of Cr (VI) detection in acidic conditions (existing as HCrO4−) caused by its low adsorption free energy, but also opening a new scenario for simple, selective, and efficient Cr (VI) detection with conjugated dye molecules.

Visual and photoelectrochemical analysis of antibiotic resistance genes enabled by surface-engineered ZIF-8@Au cascade nanozymes

The aggravation of antibiotic resistance genes (ARGs) in the environment has posed a significant global health crisis. Accurate evaluation of ARGs levels in a facile manner is a pressing issue for environmental surveillance. Here, we demonstrate a unique dumbbell-shaped cascade nanozyme for visual/photoelectrochemical (PEC) dual-mode detection of ARGs. Gold nanoparticles (AuNPs) with tunable exposed facets are controllably anchored onto ZIF-8 dodecahedrons, exhibiting glucose oxidase (GOx)-like (ZIF-8@Au/G) and peroxidase (POD)-like (ZIF-8@Au/P) activities. Upon the occurrence of ARGs, an asymmetric cascade-amplified “dumbbell” configuration is spontaneously generated via target-induced DNA hybridization, comprising GOx-like ZIF-8@Au/G with capture DNA on one side and POD-like ZIF-8@Au/P with signal DNA on the opposite side. Such a cascade nano-system can efficiently oxidize colorless 2, 2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) into its green oxidation state and synergistically decompose H2O2, realizing colorimetric/PEC dual-mode ARGs detection with a detection limit of 0.112 nM. The applicability of the present bioassay is validated through measuring ARGs in real sludge samples. This work suggests the possibility to rationally design task-specific nanozymes and develop target-responsive nano-cascade assays for environmental monitoring.

FcCe-MOF-NH2-based colorimetric and fluorometric dual-mode detection of sulfide ions

Sulfide ions, commonly present as toxic anions in industrial processes, require the creation of a convenient and reliable detection platform. In this study, we developed a dual-mode colorimetric and fluorometric method to detect sulfide ions using the cerium-ferrocene bimetal-organic framework (MOF), i.e., FcCe-MOF-NH2, which was synthesized by a common solvo-thermal approach. The FcCe-MOF-NH2 promises the peroxidase-like activity and blue emission peaked at 453 nm. In the presence of H2O2, the FcCe-MOF-NH2 catalyzed 3,3′,5,5′-tetramethylbenzidine (TMB) oxidation, yielding the blue oxidized product (oxTMB), while the fluorescence peak at 453 nm was suppressed due to the inner filter effect (IFE). The Km values of FcCe-MOF-NH2 for TMB and H2O2 were 0.099 mM and 0.179 mM, respectively, showing its good affinity with the substrates. Due to a unique redox reaction between H2O2 and S2−, the peroxidase-like activity of FcCe-MOF-NH2 was markedly suppressed, leading to fluorescence restoration. Hence, the colorimetric and fluorometric dual-mode detection of S2− was realized, exhibiting a linear range of 0.5–100 μM and 0.2–60 μM with a detection limit of 0.43 μM and 0.078 μM, respectively. The developed platform was successfully applied to the detection of S2− in actual water samples.

A dual-responsive sensor derived from carbonized polymer dots for the determination of cyanidin-3-O-glucoside

Accurate detection of cyanidin-3-O-glucoside (C3G) is crucial for ensuring food safety and optimizing quality control measures. Dual-mode sensing provides a robust approach to achieve enhanced accuracy in detection; however, the utilization of dual-mode detection for C3G remains largely unexplored. The present study introduced a novel, simple, and versatile nanomaterial carbonized polymer dots (CPDs), which harnessed the exceptional spectral properties of CPDs to achieve colorimetric-fluorescence dual-mode sensing of C3G. In the presence of C3G, the fluorescence of CPDs was quenched, resulting in a visible blue color to the naked eye. The utilization of distinct signal generation mechanisms enabled simultaneous acquisition of two independent signals, thereby providing self-verification functionality and enhancing reliability and accuracy. This dual-mode sensor exhibited high specificity, exceled in colorimetric and fluorescence detection, and was well-suited for precise identification of C3G in complex samples. It was poised to emerge as a highly sensitive and dependable tool for food safety analysis. This research project showcased the immense potential of CPDs as an efficient optical sensor while imparting invaluable insights for future C3G detection.

Bifunctional Tb(III)-modified Ce-MOF nanoprobe for colorimetric and fluorescence sensing of α-glucosidase activity

α-Glucosidase, which directly involves in the metabolism of starch and glycogen and causes an increase in blood sugar level, is the major target enzyme for the precaution and therapy of type II diabetes. Based on the previous work, we adopted a post-synthetic modification method to encapsulate Tb3+ into Ce-MOF nanozyme which owned mixed valence states. Tb@Ce-MOF displayed induced luminescence characteristic and exceptional oxidase-like activity that could oxidize colorless 3,3′,5,5′-tetramethylbenzidine (TMB) to blue ox-TMB. α-Glucosidase can hydrolyze the substrate l-ascorbic acid-2-O-α-d-glucopyranosyl (AAG) to generate ascorbic acid (AA), which could increase the Ce3+/Ce4+ redox valence mode in Tb@Ce-MOF, leading to the inhibition of the allochroic reaction of TMB and the decreased absorption of ox-TMB at 652 nm. The energy transfer (EnT) process from Ce3+ to Tb3+ will enhance due to the increased Ce3+/Ce4+ mode in Tb@Ce-MOF, which will result in an enhanced fluorescence signal of Tb@Ce-MOF at 550 nm. But the addition of inhibitor acarbose will inhibit the above process. We have constructed a dual-mode detection platform of α-glucosidase and its inhibitor via colorimetric and fluorometric method. The linear range of α-glucosidase were 0.01–0.5 U/mL (colorimetric mode) and 0.8–1.5 U/mL (fluorometric mode), respectively, with a detection limit as low as 0.0018 U/mL. Furthermore, our approach was also successfully employed to the analysis of α-glucosidase in serum samples.

Two swords combination: Smartphone-assisted ratiometric fluorescent and paper sensors for dual-mode detection of glyphosate in edible malt

The long-term and excessive use of glyphosate (GLY) in diverse matrices has caused serious hazard to the human and environment. However, the ultrasensitive detection of GLY still remains challenging. In this study, the smartphone-assisted dual-signal mode ratiometric fluorescent and paper sensors based on the red-emissive gold nanoclusters (R-AuNCs) and blue-emissive carbon dots (B-CDs) were ingeniously designed accurate and sensitive detection of GLY. Upon the presence of GLY, it would quench the fluorescence of B-CDs through dynamic quenching effect, and strengthen the fluorescence response of R-AuNCs due to aggregation-induced enhancement effect. Through calculating the GLY-induced fluorescence intensity ratio of B-CDs to R-AuNCs by using a fluorescence spectrophotometer, low to 0.218 μg/mL of GLY could be detected in lab in a wide concentration range of 0.3–12 μg/mL with high recovery of 94.7–103.1% in the spiked malt samples. The smartphone-assisted ratiometric fluorescent sensor achieved in the 96-well plate could monitor 0–11 μg/mL of GLY with satisfactory recovery of 94.1–107.0% in real edible malt matrices for high-throughput analysis. In addition, a portable smartphone-assisted ratiometric paper sensor established through directly depositing the combined B-CDs/R-AuNCs probes on the test strip could realize on-site measurement of 2–8 μg/mL of GLY with good linear relationship. This study provides new insights into developing the dual-signal ratiometric sensing platforms for the in-lab sensitive detection, high-throughput analysis, and on-site portable measurement of more trace contaminants in foods, clinical and environmental samples.

Reactive oxygen species independent oxidase like nanozyme for dual-mode analysis of α-glucosidase

Designing highly sensitive and selective assay for analyzing α-glucosidase activity is of critical value for diagnosis of related diseases. Herein, we proposed a biomineralization synthetic route to construct bovine serum albumin templated hybrid nanomaterials of Au nanoclusters (Au NCs) and oxygen deficient manganese dioxide (indicated as BAM). BAM exhibits ultra-fast oxidase (OXD)-like activity that directly oxidized TMB to generate product. Unexpected, the OXD-like activity of BAM is not relied on the reactive oxygen species or dissolved molecular oxygen, which has rarely been reported. The superior OXD-like activity of BAM is derived from the strong interactions between Au NCs and MnO2-x nanosheets that contributes to the partial reduction of MnO2-x and increase of Au(Ⅰ) species. And the catalytic mechanism is related to electron transfer from TMB to MnO2-x with Au NCs as intermediates. The analysis of α-glucosidase activity has been realized by BAM and 2-O-a-D-glucopyranosyl-L-ascorbic acid (AA2G) as the catalytic substrate with dual mode. The AA2G can be hydrolyzed by α-glucosidase into AA, which can obviously inhibit the oxidation of TMB and recover the fluorescence of Au NCs. And the inhibition ratio and recovery efficacy are related the activity of α-glucosidase. Hence, the activity of α-glucosidase can be analyzed by the changes of the signal of absorbance or fluorescence. The dual-mode detection can prevent false negative/ positive results, satisfying different demands in various analytical situation.

Colorimetric/electrochemical dual mode detection ascorbic acid based Au@PdNi nanozyme

The low activity of nanozymes poses a significant scientific challenge, limiting their application. Developing noble metal-based nanozymes with high activity is considered as an effective strategy to address this issue. In this study, core–shell Au@PdNi nanozyme was synthesized by co-precipitating Pd2+ and Ni2+ on Au cores. The oxidase (OXD)-like property of Au@PdNi was thoroughly investigated, revealing a specific activity reaching 194.2 U mg−1. The high OXD-like activity was attributed to several factors elucidated through experimental analysis and Density Functional Theory (DFT) calculations. Firstly, the core–shell structure of Au@PdNi provides a substantial surface area for catalytic reactions. Secondly, the presence of nickel enhances the current density of the material, augmenting its catalytic activity. Lastly, the electronic interplay between the Au core and the PdNi shell layer improves the binding and reaction kinetics with the target substrate. The Au@PdNi nanozyme demonstrates remarkable performances in colorimetric and electrochemical detection of ascorbic acid (AA), exhibiting high sensitivity and selectivity. Moreover, a portable electrochemical sensor was fabricated for the determination of AA in spiked fruit samples, demonstrating satisfactory recovery rates in real sample analysis.

A liposome encapsulated methylene blue-mediated electrochemical and UV–visible dual mode split-type immunoassay for the detection of 17β-estradiol

Herein, we fabricated an electrochemical (EC) and UV–visible absorption (UV–vis) dual mode split-type immunoassay for the detection of 17β-estradiol (E2), which was mediated by liposome encapsulated methylene blue (MB@lip). MB molecule acted as the probe in the EC and UV–vis absorption dual mode detections, and its release was controlled by liposome. The competitive immune recognition was conducted between the E2 in the sample and E2 conjugated bovine serum protein (E2-BSA) adsorbed on the 96-wells plate in combining with E2 antibody labeled with MB@lip (E2-Ab/MB@lip). MB molecule could be released from the resulting immune composite of E2-BSA/E2-Ab/MB@lip in the presence of Triton X-100, and quantified by UV–vis and EC methods. The three-dimensional cross-linked reduced graphene oxide/Ti3C2 (3D-rGO/Ti3C2) aerogel was prepared through hydrothermal method, then complexed with the electroactive anthraquinone (AQ) and used as the electrode modified material. The AQ/3D-rGO/Ti3C2 composite had high surface area and provided abundant adsorption sites for MB, and the displacement/competitive behavior between AQ and MB could dexterously achieve the ratiometric EC detection of E2. In addition, the inherent blue color of MB allowed it to be analyzed by UV–vis absorption method. The proposed dual mode detection method exhibited broad linear ranges of 0.1 pg mL−1 to 50 ng mL−1 (by UV–vis) and 0.03 pg mL−1 to 50 ng mL−1 (by EC) for E2 detection, and the detection limits were 0.023 pg mL−1 (S/N = 3) and 8.0 fg mL−1 (S/N = 3), respectively. Moreover, the proposed immunoassay exhibited good practicability and was applied to monitor E2 in milk and serum successfully.

Multifunctional 2D hemin-bridged MOF for the efficient removal and dual-mode detection of organophosphorus pesticides.

The high-residual and bioaccumulation property of organophosphorus pesticides (OPs) creates enormous risks towards the ecological environment and human health, promoting the research for smart adsorbents and detection methods. Herein, 2D hemin-bridged MOF nanozyme (2D-ZHM) was fabricated and applied tothe efficient removal and ultrasensitive dual-mode aptasensing of OPs. On the one hand, the prepared 2D-ZHM contained Zr-OH groups with high affinity for phosphate groups, endowing it with selective recognition and high adsorption capacity for OPs (285.7mgg-1 for glyphosate). On the other hand, the enhanced peroxidase-mimicking biocatalytic property of 2D-ZHM allowed rapid H2O2-directed transformation of 3,3',5,5'-tetramethylbenzidine to oxidic product, producing detectable colorimetric or photothermal signals. Using aptamers of specific recognition capacity, the rapid quantification of two typical OPs, glyphosate and omethoate, was realized with remarkable sensitivity and selectivity. The limit of detections (LODs) of glyphosate were 0.004nM and 0.02nM for colorimetric and photothermal methods, respectively, and the LODs of omethoate were 0.005nM and 0.04nM for colorimetric and photothermal methods, respectively. Theconstructed dual-mode aptasensing platform exhibited outstanding performance for monitoring OPs in water and fruit samples. This work provides a novel pathway to develop MOF-based artificial peroxidase and integrated platform for pollutant removal and multi-mode aptasensing.

Recognition mechanism of split T-2 toxin aptamer coupled with reliable dual-mode detection in peanut and beer

T-2 toxin is a highly poisonous trichothecene and a well-known contaminant in cereal grains and cereal-based products, hence it is essential to design a simple, reliable, and precise detection mechanism for ensuring food safety and human health. In response to this imperative, we innovatively designed an unreported split T-2 toxin aptamer probe, and the cooperative binding mechanism of the split aptamer to T-2 was first investigated. Based on these, a dual-mode fluorescence (FL) and fluorescence polarization (FP) aptasensor was developed for T-2 toxin detection in peanut and beer samples. The results showed an excellent detection property of the aptasensor, indicating a linear range of 0.1–20 nM and 0.2–50 nM at a detection limit of 0.1 nM, 0.12 nM for FL and FP signals, respectively. In actual sample assays, recoveries of 101.7%–115.2%, 109.8%–121.6% for FL and FP mode, respectively, were reached in peanuts, whereas recoveries ranged from 81.0% -124.0%, 94.1%–107.8% for FL and FP mode in beer. This designed dual-mode biosensor not only showed excellent performances but also verified each other and proved the reliability of binary split aptamer molecular probes.