Engineering an Enzymatic Cascade Catalytic Smartphone-Based Sensor for Onsite Visual Ratiometric Fluorescence-Colorimetric Dual-Mode Detection of Methyl Mercaptan

Highly selective fluorescence turn-on sensor for·thiol compounds detection

As a kind of commonly-used synthetic materials for many pesticides, thiol compounds, once being leaked, can cause serious harm to the environment and humans. Therefore, the efficient detection of thiol compounds is essential. In this study developed a turn-on fluorescent probe (Cu@Zn-CP) for the highly sensitive fluorescence detection of thiol compounds. The probe was constructed based on a zinc coordination polymer (Zn-CP), whose fluorescence was quenched through the effective doping of Cu2+ ions. After the introduction of methyl thioglycolate (MTC), a rapid fluorescence turn-on response was generated within 90 s with a low detection limit of 23 ppb. Even after being reused for five cycles, the sensor maintains excellent detection performance and demonstrates good recyclability. It can also detect MTC in river water, with a spike recovery rate between 98-103 %. Furthermore, the designed Cu@Zn-CP exhibits good universality for detecting multifarious thiol compounds, including L-cysteine, glutathione, monothioglycerol, and 2-hydroxy-1-ethanethiol. This result provides a potential recyclable fluorescent sensor for thiol compounds.

Colorimetric aptasensor based on self-screened aptamers and cascaded catalytic reaction for the detection of quarantine plant bacteria

Quarantine plant bacteria (QPB) are significant component of invasive alien species that result in substantial economic losses and serious environmental damage. Herein, a colorimetric aptasensor has been proposed based on the sandwich structure and the cascaded catalytic strategy for on-site detecting Xanthomonas hyacinthi, a type of QPB, in natural environments. The self-screened aptamer obtained through SELEX can bind to specific sites on the surface of viable organism with high affinity and specificity, which guarantees the selectivity of aptasensor. As an important part of the aptasensor, MIL-88-NH2(Fe) not only acts as a multifunctional carrier for both aptamers and glucose oxidase, but also catalyzes enzyme-like reaction because of specific surface area, amino and peroxidase-like activity. The present of Xanthomonas hyacinthi can trigger the formation of a sandwich structure and the occurrence of cascade catalytic reaction, enabling the detection with UV-Vis spectra and naked eyes. The proposed aptasensor presents a low detection limit of 2 cfu/mL and a wide linear range of 10 -107 cfu/mL. Compared to traditional detection methods for QPB, the reasonable design, high selectivity and convenience significantly improve the detection efficiency and contribute to environmental protection.

Enzyme- and label-free cascade isothermal amplification aptasensor for the ultrasensitive detection of ochratoxin A

BACKGROUND

Ultrasensitive detection is crucial for the early warning and intervention of risk factors, ultimately benefiting the environment and human health. Low levels of ochratoxin A (OTA) present a hidden yet significant threat, and rapid detection via high-performing biosensors is therefore essential.

RESULTS

A cascade isothermal amplification aptasensor (CIA-aptasensor) was designed for OTA detection. On the surface of a magnetic bead probe, the OTA level was converted into positively correlated trigger cDNA through its competitive binding with OTA-Apt. The released trigger cDNA activated catalytic hairpin assembly followed by coupling with a hybridization chain reaction to achieve CIA. After adding graphene oxide and SYBR Green I, the background interference was eliminated to specifically obtain OTA-related fluorescence. The ultrasensitive limit of detection was 0.22 pg mL-1, an improvement of 1368-fold over conventional enzyme-linked aptamer sorbent assay by the same OTA-Apt, demonstrating satisfactory reliability and practicability. Thus, the CIA-aptasensor provides an enzyme- and label-free simplified homogeneous system with minimal background interference using isothermal conditions.

SIGNIFICANCE

This study provides a polymerase chain reaction-like approach for enhancing the sensitivity and performance of a biosensor, which could be extended for the application of CIA and label-free signaling strategy to other risk factors.

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.

Sensitive colorimetric detection of Vibrio vulnificus based on target-induced shielding against the peroxidase-mimicking activity of CeO2@PtRu nanozyme

Vibrio vulnificus infection caused by contaminated aquatic products and seawater can lead to severe disease and high mortality. The development of a rapid and sensitive detection method for Vibrio vulnificus is vital to effectively prevent infection in advance. In this study, CeO2@PtRu with high peroxidase activity was used to construct a colorimetric immunoassay for Vibrio vulnificus detection by conjugating polyclonal antibodies via the biotin-streptavidin system. The developed colorimetric biosensor for Vibrio vulnificus demonstrated rapid operability and good sensitivity with a detection range from 104 CFU/mL to 109 CFU/mL, and the limit of detection (LOD) is 193 CFU/mL. Moreover, the colorimetric biosensor showed excellent specificity and good recoveries from 98.70% to 102.10% with RSD < 7.45% for spiked real samples. This novel CeO2@PtRu-based colorimetric biosensor has great application potential for the sensitive detection of Vibrio vulnificus in seafood.

Triple modal aptasensor arrays driven by CHA-mediated DNAzyme for signal-amplified atrazine pesticide accumulation monitoring in agricultural crops

Developing sensors with high selectivity and sensitivity is of great significance for pesticide analysis in environmental assessment. Herein, a versatile three-way sensor array was designed for the detection of the pesticide atrazine, based on the integration of catalytic hairpin assembly (CHA) amplification and three-mode signal transducers. With atrazine, CHA was triggered to generate abundant G-quadruplex. The produced G-quadruplex hybrid could assemble with thioflavin T (TFT) or hemin to mimic enzyme and induce the fluorescence enhancement by TFT, or the colorimetric increase by the oxidized chromogenic substrate and the naked-eye color change by inhibiting the L-cysteine-mediated aggregation of gold nanoparticles. A distinctive three-mode array was successfully constructed with convenience, on-site accessibility and high sensitivity for enzyme-free practical analysis of atrazine. It is also effective and reliable for analyzing real samples including paddy water, paddy soil and polished rice. The detection limits for atrazine were as low as 7.4 pg/mL by colorimetric observation and 0.25 pg/mL by fluorescent detection. Furthermore, the array was exploited to monitor the residue, distribution and bioaccumulation of atrazine in maize and rice for food security and environmental assessment. Hence, this work presented a versatile example for sensitive and on-site all-in-one pesticide analysis arrays with multiple signal report modes.

Ligand-Induced Red-Emitting Copper Nanoclusters for Selective Fluorescence Determination of Aluminum Ions

Monitoring levels of excessive aluminum ions (Al3+) is crucial as it can harm the immune system, reduce enzyme activity, cause cell death, and damage environmental and biological systems. Developing a fast and efficient Al3+ ion determination method is the key to addressing this issue. In this work, red-emitting fluorescent copper nanoclusters (CuNCs) were synthesized using N-acetyl-l-cysteine (NAC) as a ligand and CuCl2·2H2O through a facile procedure. The NAC-CuNCs exhibited a large Stokes shift and displayed remarkable luminescence properties. A method for detecting Al3+ through a fluorescence probe was proposed. Its fluorescence mechanism was also explored. The probe showed rapid responsiveness (within 1 min) to Al3+ ion determination. The detection limit for Al3+ was found to be 19.7 nM, which is significantly lower than the WHO's value and most reports, with a linear range of 0-52.9 μM. The determination of Al3+ concentrations in actual water using the fluorescence probe yielded satisfactory outcomes. Moreover, the visual detection of Al3+ ions was also achieved through a smartphone, which can enhance its fast and practical detection.

AIE fluorescent nanozyme-based dual-mode biosensor for analysis of the bioactive component hypoxanthine in meat products

The development of facile, low-cost reliable, and precise onsite assays for the bioactive component hypoxanthine (Hx) in meat products is significant for safeguarding food safety and public health. Herein, we proposed a smartphone-assissted aggregation-induced emission (AIE) fluorogen tetraphenylethene (TPE)-incorporated amorphous Fe-doped phosphotungstates (Fe-Phos@TPE) nanozyme-based ratiometric fluorescence-colorimetric dual-mode biosensor for achieving the onsite visual detection of Hx. When the Hx existed, xanthine oxidase (XOD) catalyzed Hx into H2O2 to be further catalyzed into •OH by the prominent peroxidase activity of Fe-Phos@TPE at pH = 6.5, resulting in the oxidization of nonfluorescent o-phenylenediamine (OPD, naked-eye colorless) to be yellow fluorescent emissive 2,3-diaminophenazine (DAP, naked-eye dark yellow) at 550 nm as well as the intrinsic blue fluorescence of Fe-Phos@TPE at 440 nm to be decreased via inner-filter effect (IFE) action, thereby realizing a multi-enzyme cascade catalytic reaction at near-neutral pH to overcome the traditional acidity dependence-induced time-consuming and low sensitivity troublesome.

A Versatile Visual Molecular Imprinting-Driven Switchable Nanozyme Activity-Based Trimodal Assay and Logic Gate Circuits of Ethyl Carbamate

Concerns regarding the hazard of the carcinogenic ethyl carbamate (EC) have driven attempts to exploit efficient, timely, straightforward, and economic assays for warning early food safety. Here, we proposed a novel molecularly imprinted polymer Co@MOF-MIP, with a high peroxidase (POD)-like activity and a bright blue fluorescence emission, to develop a versatile visual assay for colorimetric, fluorescent, and photothermal trimodal detection and logic gate outputting of EC. Briefly, the POD-like activity of Co@MOF-MIP made it to decompose H2O2 into ·OH for oxidizing colorless 3,3',5,5'-tetramethylbenzidine (TMB) into a blue oxTMB, resulting in a 660 nm irradiated photothermal effect and bursting the blue fluorescence of Co@MOF-MIP via inner filter effect, observing a decreased fluorescence signal together with an increased colorimetric and 660 nm irradiated photothermal signals. However, EC could specifically fill the imprinted cavities of Co@MOF-MIP to block the catalytic substrates TMB and H2O2 out of Co@MOF-MIP for further reacting with the inside catalytic center of Co2+, resulting in the transformation suppressing of TMB into oxTMB, yielding an EC concentration-dependent trimodal responses in fluorescence signal enhancement, colorimetric, and 660 nm irradiated photothermal signal decreases. Assisted by the portable devices such as smartphones and hand-held thermal imagers, a visual onsite portable trimodal analytical platform was proposed for EC fast and accurate detection with the low detection limits of 1.64, 1.24, and 1.78 μg/L in colorimetric, fluorescent, and photothermal modes, respectively. Interestingly, these reactive events could be programmed by the classical Boolean logic gate analysis to offer a novel promising avenue for the big data Internet of Things monitoring and warning early residual EC in a more intelligent, dynamical, fast, and accurate manner, safeguarding food safety.

Dual response signal CdTe QDs@ZIF-8 with butterfly spectrum for dual-mode fluorescence/colorimetric detection of tetracycline in animal feeds

In this study, a ratiometric fluorescent sensor CdTe QDs@ZIF-8 with butterfly spectra is successfully constructed by in situ encapsulating mercaptopropionic acid-modified CdTe quantum dots in zeolitic imidazolate framework-8 (ZIF-8) with a simple strategy, and used for the detection of tetracycline in fluorescence/smartphone colorimetry dual-mode. ZIF-8 not only reduces the agglomeration of the quantum dots but also surprisingly generates a new green fluorescence signal at 524 nm while the red fluorescence of the CdTe quantum dots at 650 nm quenches when tetracycline is added. The two opposing fluorescence signals create a butterfly-shaped fluorescence spectrum, allowing the sensor to detect tetracycline over a linear range of 0-70 μM with the detection limit (LOD) of 0.0155 μM by using a ratiometric fluorescence technique. What is more, based on the obvious color change of the fluorescent sensor gradually from red to green under UV light, a highly stable point-of-care testing sensor has been developed for on-site detection of tetracycline through color recognition by smartphones, which can be used for real-time detection of this antibiotic in the range of 0-1000 μM with the LOD of 0.0249 μM. This work provides a simple and efficient method for the on-site detection of tetracycline.

Programming of a Portable Digital Monitoring System-Integrated DNA Aptamer Reversely Regulated Oxidase-Like Nanozyme for Real-Time Dynamic Analysis of Atmospheric Perfluorooctanoic Acid

Timely and efficient analysis of the fluorinated per- and polyfluoroalkyl substances (PFAS) in an atmospheric environment is critical to environmental pollution traceability, early warnings, and governance. Here, a portable, reliable, and intelligent digital monitoring device for onsite real-time dynamic analysis of atmospheric perfluorooctanoic acid (PFOA) is proposed. The sensing mechanism is attributed to the oxidase-like activity of PtCoNPs@g-C3N4 that is reversely regulated by the surface modification of a PFOA-recognizable DNA aptamer, engineering a PFOA-activated oxidase-like activity of nanozyme (Apt-PtCoNPs@g-C3N4) to combine the nonfluorescence o-phenylenediamine (OPD) as the dual-modality response system. The present PFOA interacts with its DNA aptamer and dissociates from the surface of Apt-PtCoNPs@g-C3N4, restoring the oxidase-like activity of PtCoNPs@g-C3N4 to oxidize OPD into yellow fluorescence 2,3-diphenylaniline (DAP), thereby observing a PFOA-triggered colorimetric as well as fluorescence dual-modality change. Then, a hydrogel kit-programmed Apt-PtCoNPs@g-C3N4 + OPD system is used as the sensitive element to incorporate into this homemade portable device, automatically gathering and processing the PFOA-triggered hydrogel colorimetric and fluorescence image gray values by our self-weaving software, ultimately realizing the onsite real-time dynamic analysis of atmospheric PFOA surrounding a fluorochemical production plant. This work provides a direction and theoretical foundation for designing portable onsite screening devices that cater to other atmospheric contaminants detection requirements.

Smartphone-assisted array discrimination of sulfur-containing compounds and colorimetric-fluorescence dual-mode sensor for detection of 1,4-benzenedithiol based on peroxidase-like nanozyme g-C3N4@Cu, N-CDs

Present work reported a novel nanozyme g-C3N4@Cu, N-CDs with excellent peroxidase-like activity obtained by loading Cu and N co-doped carbon dots on g-C3N4 (graphitic carbon nitride). g-C3N4@Cu, N-CDs can catalyze H2O2 to generate hydroxyl radical •OH, which oxidizes o-phenylenediamine to 2,3-diaminophenazine, which emits orange fluorescence under ultraviolet light irradiation. The experimental results confirmed that 1,4-benzenedithiol (BDT) could inhibit the peroxidase-like activity of g-C3N4@Cu, N-CDs. Based the principle above, a colorimetric-fluorescence dual-mode sensor for rapidly sensing of BDT was creatively constructed with assisting of a smartphone. The sensor showed excellent linearity over ranges of 0.75-132 μM and 0.33-60.0 μM with detection limits of 0.32 μM and 0.25 μM for colorimetric and fluorescence detection, respectively. Moreover, a smartphone-assisted colorimetric array sensor was constructed to distinguish six sulfur-containing compounds according to the difference in the degree of inhibition of nanozyme activity by different sulfur-containing compounds. The array sensor could distinguish sulfur-containing compounds at low concentration as low as 0.4 μM. The results validated that the designed sensor was a convenient and fast platform, which could be utilized as a reliably portable tool for the efficient and accurate detection of BDT and the discrimination of multiple sulfur compounds in real water samples.

Wearable, Biocompatible, and Dual-Emission Ocular Multisensor Patch for Continuous Profiling of Fluoroquinolone Antibiotics in Tears

The abuse or misuse of antibiotics in clinical and agricultural settings severely endangers human health and ecosystems, which has raised profound concerns for public health worldwide. Trace detection and reliable discrimination of commonly used fluoroquinolone (FQ) antibiotics and their analogues have consequently become urgent to guide the rational use of antibiotic medicines and deliver efficient treatments for associated diseases. Herein, we report a wearable eye patch integrated with a quadruplex nanosensor chip for noninvasive detection and discrimination of primary FQ antibiotics in tears during routine eyedrop treatment. A set of dual-mode fluorescent nanoprobes of red- or green-emitting CdTe quantum dots integrated with lanthanide ions and a sensitizer, adenosine monophosphate, were constructed to provide an enhanced fluorescence up to 45-fold and nanomolar sensitivity toward major FQs owing to the aggregation-regulated antenna effect. The aggregation-driven, CdTe-Ln(III)-based microfluidic sensor chip is highly specific to FQ antibiotics against other non-FQ counterparts or biomolecular interfering species and is able to accurately discriminate nine types of FQ or non-FQ eyedrop suspensions using linear discriminant analysis. The prototyped wearable sensing detector has proven to be biocompatible and nontoxic to human tissues, which integrates the entire optical imaging modules into a miniaturized, smartphone-based platform for field use and reduces the overall assay time to ∼5 min. The practicability of the wearable eye patch was demonstrated through accurate quantification of antibiotics in a bactericidal event and the continuous profiling of FQ residues in tears after using a typical prescription antibiotic eyedrop. This technology provides a useful supplement to the toolbox for on-site and real-time examination and regulation of inappropriate daily drug use that might potentially lead to long-term antibiotic abuse and has great implications in advancing personal healthcare techniques for the regulation of daily medication therapy.

Three-Dimensional DNA Hydrogel Mediated Dual-Mode Sensing Method for Quantification of Epithelial Cell Adhesion Molecule in Biological Fluid Samples

Monitoring changes in the expression of marker proteins in biological fluids is essential for biomarker-based disease diagnosis. Epithelial cell adhesion molecule (EpCAM) has been identified as a broad-spectrum biomarker for various chronic diseases and as a therapeutic target. However, the development of simple and reliable methods for quantifying EpCAM changes in biological fluids faces challenges due to the variability of its expression across different diseases, the presence of soluble forms, and matrix effects. In this paper, a surface-enhanced Raman scattering (SERS)-fluorescence (FL) dual-mode sensing method was established for quantification of trace EpCAM in biological fluids based on bimetallic Au@Ag nanoparticles and nitrogen-doped quantum dots encapsulated DNA hydrogel hybrid with graphene oxide (Au@Ag-NQDs/GO). The DNA hydrogel was constructed based on three-dimensional (3D) structure DNA-mediated strategy using an aptamer DNA (AptDNA) linker. The interaction of the AptDNA with EpCAM triggered the disassembly of the DNA hydrogel. Consequently, the release of Au@Ag nanoparticles induced an "on-off" switch in the SERS signal while the weakened FL quenching effect in Au@Ag-NQDs/GO system achieved "off-on" switch of FL signal, enabling the simultaneous SERS-FL quantification of EpCAM. The established dual-mode method exhibited outstanding sensitivity and stability in quantifying EpCAM in the range of 0.5-60.0 pg/mL, with the limits of detection (LODs) of SERS and FL as 0.17 and 0.35 pg/mL, respectively. When applied for real sample analysis, the method showed satisfactory specificity and recoveries in cancer cells lysate, serum, and urine samples with RSDs of 2.8-6.3%, 4.0-6.3%, and 2.8-5.7%, respectively. The developed SERS-FL sensing method offered a sensitive, reliable, and practical quantification strategy for trace EpCAM in diverse biological fluid samples, which would benefit the early diagnosis of disease and further health management.

RuZn NPs with electroactivity and oxidase-like property for dual-mode anti-cancer drug monitoring

6-mercaptopurine (6-MP) as the effective anti-cancer drug was used for the treatment of Crohn's disease and acute lymphoblastic leukaemia, but the response to maintenance therapy was variable with individual differences. In order to control the dosage and decrease the side effects of 6-MP, a sensitive and stable assay was urgently needed for 6-MP monitoring. Herein, RuZn NPs with electrochemical oxidation property and oxidase-like activity was proposed for dual-mode 6-MP monitoring. Burr-like RuZn NPs were prepared and explored to not only exhibit an electrochemical oxidation signal at 0.78 V, but also displayed excellent oxidase-like performances. RuZn NPs were utilized for the dual-mode monitoring of 6-MP, attributing to the formation of Ru-SH covalent bonding. The colorimetric method showed good linearity from 10 μM to 5 mM with the limit of detection (LOD) of 300 nM, while the electrochemical method provided a higher sensitivity with the LOD of 37 nM in range from 100 nM to 200 μM. This work provided a new way for the fabrication of dual-functional nanotags with electroactivity and oxidase-like property, and opened a dual-mode approach for the 6-MP detection applications with complementary and satisfactory results.

Mechanistic investigation and dual-mode colorimetric-chemiluminescent detection of glyphosate based on the specific inhibition of Fe3O4@Cu nanozyme peroxidase-like activity

In this study, a dual-mode colorimetric/CL nanosensor was developed for glyphosate detection based on the specific inhibition of Fe3O4@Cu peroxidase-like activity. Synthesized Fe3O4@Cu exhibited high levels of peroxidase-like activity that triggered the oxidation of luminol/3,3',5,5'-tetramethyl benzidine dihydrochloride (TMB) to excited-state 3-aminophthalic acid/blue oxTMB, thereby delivering a CL signal/visible colorimetric signal, however, the presence of glyphosate inhibited this activity, resulting in a decrease in signal strength. In-depth investigation revealed that this inhibitory mechanism occurs via two pathways: one in which glyphosate chelates with Fe(III)/Cu(II) and occupy the catalytical active sites of Fe3O4@Cu, thereby decreasing the generation of OH, and another in which glyphosate competes with TMB to consume generated OH, thus reducing the oxidation of TMB. This mechanism formed the basis of our novel dual-mode colorimetric/CL glyphosate nanosensor, which achieved limits of detection (LODs) of 0.086 µg/mL and 0.019 µg/mL in tests, thus demonstrating its significant potential for on-site glyphosate monitoring.

Multiplexed colorimetry collaborated with smartphone-based image analysis for simultaneous and fast visualization of dyes in both environmental and food samples

In this work, a multiplexed colorimetric strategy was initiated for simultaneous and fast visualization of dyes using low-cost and easy-to-prepare indicator papers as sorbents. Response surface methodology (RSM) was employed to model statistically and optimize the process variables for dyes extraction and colorimetric assays. Multiplexed colorimetry was realized by virtue of synchronous color alignments from different dimensions of multiple dyes co-stained colorimetric cards under RSM-optimized conditions, and smartphone-based image analysis was subsequently performed from different modes to double-check the credibility of colorimetric assays. As concept-to-proof trials, simultaneous visualization of dyes in both beverages and simulated dye effluents was experimentally proved with results highly matched to HPLC or spiked amounts at RSM-predicted staining time as short as 50 s ∼3 min, giving LODs as low as 0.97 ± 0.22/0.18 ± 0.08 μg/mL (tartrazine/brilliant blue) for multiplexed colorimetry, which much lower than those obtained by single colorimetry. Since this is the first case to propose such a RSM-guided multiplexed colorimetric concept, it will provide a reference for engineering of other all-in-one devices which can realize synchronous visualization applications within limited experimental steps.

A simple aptamer-dye fluorescence sensor for detecting Δ9-tetrahydrocannabinol and its metabolite in urban sewage

This work developed an aptamer-dye complex as a label-free ratiometric fluorescence sensor for rapid analysis of THC and its metabolite in sewage samples. Integrated with a portable fluorescence capture device, this sensor exhibited excellent sensitivity with visualization of as low as 0.6 μM THC via naked-eye observation, and THC analysis can be accomplished within 4 min, which would be a complementary tool for quantifying THC in sewage samples to estimate cannabis consumption.

Portable hydrogel kit driven by bimetallic carbon dots nanozyme for H2O2-self-supplying dual-modal monitoring of atmospheric CH3SH

Due to the typical volatility of gaseous pollutant methyl mercaptan (CH3SH), the development of a facile, reliable, and accurate onsite environmental surveillance of highly toxic CH3SH faces many challenges, but it is critical to environmental atmosphere assessment and safeguarding public health. Here, we prepared a novel bimetallic carbon dots (Fe&Cu@CDs) nanozyme with high peroxidase-mimicking activity to design a portable hydrogel kit for onsite visual H2O2-self-supplying enzymatic cascade catalytic colorimetric and photothermal signal synergistic amplification dual-modal monitoring of CH3SH in atmospheric environment. Assisted by alcohol oxidase (AOX), CH3SH could be specifically converted into H2O2 for oxidizing chromogenic substrate 3,3',5,5'-tetramethylbenzidine (TMB) catalyzed by Fe&Cu@CDs to produce dark blue ox-TMB with absorption at 652 nm and photothermal characters. Consequently, a CH3SH concentration-dependent change both in naked-eye color and photothermal effect-triggered temperature were observed. By hybridizing AOX-assisted Fe&Cu@CDs + TMB with agarose, a H2O2-self-supplying colorimetric and photothermal signal synergistic amplification sensory hydrogel kit integrated with Color Picker APP-installed smartphone and 660 nm laser-equipped handheld thermal imager for CH3SH was proposed with acceptable results in atmospheric environment around wastepile (e.g., solid waste and food waste piles), which exhibited great potentials to further develop commercial onsite monitoring platforms in warning-early abnormal atmospheric CH3SH for safeguarding environmental health.

Machine-Learning-Assisted Aggregation-Induced Emissive Nanosilicon-Based Sensor Array for Point-of-Care Identification of Multiple Foodborne Pathogens

How timely identification and determination of pathogen species in pathogen-contaminated foods are responsible for rapid and accurate treatments for food safety accidents. Herein, we synthesize four aggregation-induced emissive nanosilicons with different surface potentials and hydrophobicities by encapsulating four tetraphenylethylene derivatives differing in functional groups. The prepared nanosilicons are utilized as receptors to develop a nanosensor array according to their distinctive interactions with pathogens for the rapid and simultaneous discrimination of pathogens. By coupling with machine-learning algorithms, the proposed nanosensor array achieves high performance in identifying eight pathogens within 1 h with high overall accuracy (93.75-100%). Meanwhile, Cronobacter sakazakii and Listeria monocytogenes are taken as model bacteria for the quantitative evaluation of the developed nanosensor array, which can successfully distinguish the concentration of C. sakazakii and L. monocytogenes at more than 103 and 102 CFU mL-1, respectively, and their mixed samples at 105 CFU mL-1 through the artificial neural network. Moreover, eight pathogens at 1 × 104 CFU mL-1 in milk can be successfully identified by the developed nanosensor array, indicating its feasibility in monitoring food hazards.

An intelligent ratiometric fluorescent assay based on MOF nanozyme-mediated tandem catalysis that guided by contrary logic circuit for highly sensitive sarcosine detection and smartphone-based portable sensing application

As the well-known test-indicator for early prostate cancer (PCa), sarcosine (SA) is closely related to the differential pathological process, which makes its accurate determination increasingly significant. Herein, we for the first time expanded the peroxidase (POD)-like property of facile-synthesized Zn-TCPP(Fe) MOF to fluorescent substrates and exploited it to ratiometric fluorescent (RF) sensing. By harnessing the effective catalytic oxidation of MOF nanozyme toward two fluorescent substrates (Scopoletin, SC; Amplex Red, AR) with contrary changes, and target-responsive (SA + SOx)/MOF/(SC + AR) tandem catalytic reaction, we constructed the first MOF nanozyme-based RF sensor for the quantitative determination of SA. Superior to previous works, the operation of this RF sensor is under the guidance of AND-(AND^NAND) contrary logic circuit. The dual-channel binary output changes (from 1/0 to 0/1) not only enable the intelligent logical recognition of SA, bringing strengthened reliability and accuracy, but also manifest the proof-of-concept discrimination of PCa individuals and healthy ones. Through recording the fluorescence alterations of SC (F465) and AR (F585), two segments of linear relationships between ratiometric values (F585/F465) and varied contents of SA are realized successfully. The LOD for SA could reach to as low as 39.98 nM, which outperforms all nanozyme-originated SA sensors reported till now. Moreover, this sensor also demonstrates high selectivity and satisfactory performance in human serum samples. Furthermore, the portable sensing of SA is realized under the assistance of smartphone-based RGB analysis, demonstrating the potential of point-of-care diagnostics of PCa in the future.

Highly Selective and Portable Fluorescence Turn-On Detection of Sc3+ in Ore and Water Based on Strong Lewis Acid-Base Coordination

Detecting scandium (Sc) with high selectivity and sensitivity is a challenging task due to its chemical similarity to other rare earth ions. Our findings show that the fluorescence of the complex fluorescent indicator calcein (CL) is quenched under acidic conditions (pH = 2), and Sc3+ strongly inhibits this process. The results demonstrate that CL forms multimers and precipitates out of the solution under acidic conditions, while Sc3+ causes a significant decrease in the scattering intensity of the solution. Additional experiments revealed that the strong Lewis acid nature of Sc3+ complexes with the carboxyl groups of CL leads to increased dispersion of CL even under acidic conditions, thus enhancing its absorption and fluorescence. The complexation ratio of Sc3+ and CL was investigated through spectral titrations and theoretical calculations. The interaction between Sc3+ and CL is the strongest among rare earth and common metal ions due to the smallest ionic radius, resulting in high selectivity. The fluorescence turn-on strategy had a linear range of 0.04 to 2.25 μM under optimal conditions, with a detection limit of 20 nM for Sc3+. The combination of 3D printing and a smartphone program allows for portable on-site analysis of Sc3+. Mineral and water samples were used to demonstrate the potential of this strategy for the rapid, selective, and sensitive analysis of low levels of Sc3+.

"Five birds one stone" tri-modal monitoring driven lab-on-magnetic aptasensor for accurate pathogen detection and enhanced germicidal application

The effective combination of ultra-precise detection and on-demand sterilization stands out as one of the most valuable antifouling methods to combat pathogenic bacteria source and ensure the environment and food safety. Herein, an innovative "five birds one stone" aptasensor has been reported. It integrates magnetic separation, tri-modal precision detection, and efficient sterilization for monitoring of Staphylococcus aureus. Firstly, as a switch of the aptasensor, aptamer-modified potassium chloride-doped carbon dots (apt/KCl@CDs) could be adsorbed onto the surface of magnetic multi-walled carbon nanotube composites (M-MWCNTs) through π-π stacking, which could be replaced by the specific binding of the target bacteria to the aptamer. The mutual interference between the nanomaterials could be eliminated by this reverse magnetosorption strategy, enhancing the test sensitivity. In addition to the fluorescence properties, the peroxidase activity possessed by apt/KCl@CDs enables the conversion of the (3,3',5,5'-tetramethylbenzidine) TMB-H2O2 colorimetric system to a photothermal modal. Then, the ultra-precision detection in the assay was achieved by the fluorescence-colorimetric-photothermal tri-modal sensing from the formation of S. aureus-apt/KCl@CDs in the supernatant. Besides, the efficient sterilization could be ensured by adsorbing the apt/KCl@CDs on the surface of S. aureus, generating toxic •OH for direct attacking cells. This was the first report that was more beneficial for bacterial eradication. The detection limits of fluorescence, colorimetric and photothermal modals were 4.81 cfu/mL, 3.40 cfu/mL and 6.74 cfu/mL, respectively. The magnetic nanoplatform integrating tri-modal detection-sterilization meets the demand for highly sensitive and precise detection in different scenarios, providing immediate control for pathogens and broad application prospects.

Biocompatible N-carbazoleacetic acid decorated CuxO nanoparticles as self-cascading platforms for synergistic single near-infrared triggered phototherapy treating microbial infections

In this work, positively charged N-carbazoleacetic acid decorated CuxO nanoparticles (CuxO-CAA NPs) as novel biocompatible nanozymes have been successfully prepared through a one-step hydrothermal method. CuxO-CAA can serve as a self-cascading platform through effective GSH-OXD-like and POD-like activities, and the former can induce continuous generation of H2O2 through the catalytic oxidation of overexpressed GSH in the bacterial infection microenvironment, which in turn acts as a substrate for the latter to yield ˙OH via Fenton-like reaction, without introducing exogenous H2O2. Upon NIR irradiation, CuxO-CAA NPs possess a high photothermal conversion effect, which can further improve the enzymatic activity for increasing the production rate of H2O2 and ˙OH. Besides, the photodynamic performance of CuxO-CAA NPs can produce 1O2. The generated ROS and hyperthermia have synergetic effects on bacterial mortality. More importantly, CuxO-CAA NPs are more stable and biosafe than Cu2O, and can generate electrostatic adsorption with negatively charged bacterial cell membranes and accelerate bacterial death. Antibacterial results demonstrate that CuxO-CAA NPs are lethal against methicillin-resistant Staphylococcus aureus (MRSA) and ampicillin-resistant Escherichia coli (AREC) through destroying the bacterial membrane and disrupting the bacterial biofilm formation. MRSA-infected animal wound models show that CuxO-CAA NPs can efficiently promote wound healing without causing toxicity to the organism.

Smartphone-assisted hydrogel platform based on BSA-CeO2 nanoclusters for dual-mode determination of acetylcholinesterase and organophosphorus pesticides

A dual-mode sensor was developed for detecting acetylcholinesterase (AChE) and organophosphorus pesticides (OPs) via bifunctional BSA-CeO2 nanoclusters (NCs) with oxidase-mimetic activity and fluorescence property. The dual-mode sensor has the characteristics of self-calibration and self-verification, meeting the needs of different detection conditions and provide more accurate results. The colorimetric sensor and fluorescence sensor have been successfully used for detecting AChE with limit of detection (LOD) of 0.081 mU/mL and 0.056 mU/mL, respectively, while the LOD for OPs were 0.9 ng/mL and 0.78 ng/mL, respectively. The recovery of AChE was 93.9-107.2% and of OPs was 95.8-105.0% in actual samples. A novel strategy was developed to monitor pesticide residues and detect AChE level, which will motivate future work to explore the potential applications of multifunctional nanozymes.

Multi-modal nanoprobe-enabled biosensing platforms: a critical review

Nanomaterials show great potential for applications in biosensing due to their unique physical, chemical, and biological properties. However, the single-modal signal sensing mechanism greatly limits the development of single-modal nanoprobes and their related sensors. Multi-modal nanoprobes can realize the output of fluorescence, colorimetric, electrochemical, and magnetic signals through composite nanomaterials, which can effectively compensate for the defects of single-modal nanoprobes. Following the multi-modal nanoprobes, multi-modal biosensors break through the performance limitation of the current single-modal signal and realize multi-modal signal reading. Herein, the current status and classification of multi-modal nanoprobes are provided. Moreover, the multi-modal signal sensing mechanisms and the working principle of multi-modal biosensing platforms are discussed in detail. We also focus on the applications in pharmaceutical detection, food and environmental fields. Finally, we highlight this field's challenges and development prospects to create potential enlightenment.

Fluorimetric determination of tetracycline antibiotics in animal derived foods using boron and nitrogen co-doped ceria-based nanoparticles

An innovative synthesis of boron and nitrogen co-doped ceria-based nanoparticles (B/N-CeFNPs) with bright blue fluorescence emission is reported using the hydrothermal method. Based on the aggregation-induced emission enhancement (AIEE) effect between B/N-CeFNPs and chlortetracycline (CTC), a rapid detection method for CTC through fluorescence enhancement was developed. In addition, through the electron transfer process (ET), fluorescence resonance energy transfer (FRET) effect and static quenching between B/N-CeFNPs and oxytetracycline (OTC), a ratio fluorescence strategy for detecting OTC was generated. The fluorescence of B/N-CeFNPs at 410 nm can be effectively quenched by OTC, and new fluorescence emission appears at a wavelength of 500 nm. B/N-CeFNPs showed good linear responses with CTC and OTC in the range 0.1-1 µM and 1-40 µM, respectively. This system was used to simultaneously detect the CTC and OTC in milk and honey, realizing multi-residues detection of TCs in actual samples by using the same ceria-based fluorescence nanomaterial.

Ultrasensitive Dual-Mode Visual/Photoelectrochemical Bioassay for Antibiotic Resistance Genes through Incorporating Rolling Circle Amplicons into a Tailored Nanoassembly

As emerging contaminants in the environment, antibiotic resistance genes (ARGs) have aroused a global health crisis and posed a serious threat to ecological safety and human health. Thus, efficient and accurate onsite detection of ARGs is crucial for environmental surveillance. Here, we presented a colorimetric-photoelectrochemical (PEC) dual-mode bioassay for simultaneous detection of multiple ARGs by smartly incorporating rolling circle amplification (RCA) into a stimuli-responsive DNA nanoassembly, using the tetracycline resistance genes tetA and tetC as models. The tailored DNA nanoassembly containing RCA amplicons hybridized with specific signal probes: CuO nanoflowers-anchored signal DNA1 and HgO nanoparticles-anchored signal DNA2, respectively. Upon exposure to an acidic stimulus, numerous Cu2+ and Hg2+ were released, serving as the reporting agent of colorimetric/PEC dual-mode assay. The released Cu2+ and Hg2+ induced localized surface plasmon resonance shifts in Au nanorods and triangular Ag nanoplates through an etching process, respectively, enabling visual analysis of ARGs with distinguishing color changes. Meanwhile, numerous Cu2+ and Hg2+ triggered the amplified PEC variations via reacting with the photoactive layers of CuS/CdS and ZnS, respectively. Thus, a rapid and ultrasensitive colorimetric/PEC dual-mode detection of multiple ARGs was achieved with the detection limit down to 17.2 aM. Furthermore, such dual-mode bioassay could discriminate single-base mismatch and successfully determine ARGs in E. coli plasmids and sludge samples, holding great promise for point-of-care genetic diagnostics.

A fluorescent method for bisphenol A detection based on enzymatic oxidation-mediated emission quenching of silicon nanoparticles

As a common raw material of industrial products, bisphenol A (BPA) is widely used in the production of food contact materials, and there is a high risk of exposure in food. However, BPA is a well-known endocrine disruptor and poses a serious threat to human health. Herein, a fluorescent sensing platform of BPA based on enzymatic oxidation-mediated fluorescence quenching of silicon nanoparticles (SiNPs) is established and used to the detection of BPA in food species. The SiNPs are prepared with a facile one-step synthesis and emit bright green fluorescence. BPA can be oxidized by horseradish peroxidase (HRP) and hydrogen peroxide (H2O2) to form a product which can quench the fluorescence of SiNPs through electron transfer. There is a good linear relationship between the fluorescence intensity and BPA concentration in the range of 1-100 μM. Therefore, a fluorometry of BPA is established with a low limit of detection (LOD) of 0.69 μM. This method has been applied to the determination of BPA in mineral drinking water, orange juice, and milk with satisfactory results. The fluorescent sensor of BPA based on SiNPs has favorable application foreground in the field of food safety analysis.

Rhodamine B functionalized silver nanoparticles paper discs as turn-on fluorescence sensor, coupled with a smartphone for the detection of microbial contamination in drinking water

The precise detection of pathogenic microorganisms is crucial for the reduction of water-borne diseases. Herein, a filter-paper-based florescent chemosensor was fabricated for the detection of Escherichia coli and Staphylococcus aureus contamination exploiting protein-DNA interaction between the target and a specific probe. The sensing mechanism involved the self-assembly of Rhodamine B (RhB) on silver nanoparticles (AgNPs) surface that was labeled with a single-stranded DNA probe. This causes the fluorescence quenching of RhB by a distant-dependant process. The hybridization between pathogen-specific probe and bacterial surface protein causes the release of fluorescence of RhB, which was observed under UV light. For paper-based bio-surface preparation, the mixture comprising RhB-AgNP-ssDNA was drop-casted on filter paper discs. The conditions were optimized using isolated genomic DNA of the microbes. The method was applied for E.coli detection using an eae gene-based probe targeting intimin protein and S. aureus detection using tuf gene-based probe targeting EF-tuf protein on the microbe's surface. The chemosensor had a notable specificity and selectivity for E.coli, and S. aureus, with detection limits of 0.6 × 108 and 0.37 × 103 CFU/mL respectively. Moreover, the sensor was tested on real water samples, which presented excellent reproducibility of results (RSD ≤ 0.24%). Furthermore, the gradient change of fluorescence was captured by a smartphone, which allows direct detection of pathogens in a sensitive semi-quantitative way without the need for expensive instruments. The designed chemosensor can serve as a simple, inexpensive, and rapid method for the on-site detection of microbial contamination in drinking water.

Cation Exchange Reaction-Mediated Photothermal and Polarity-Switchable Photoelectrochemical Dual-Readout Biosensor

Cation exchange (CE) is a burgeoning method for controlled crystal synthesis; however, its applications in bioanalysis are still in their infancy. Herein, we explored the transformation of ZnIn2S4 in properties after the CE reaction with Cu2+ ions; furthermore, the discrepancy was employed to design a dual-readout detection system of photothermal and polarity-switchable photoelectrochemical (PEC) immunoassays to realize reliable detection of carcinoembryonic antigen (CEA). In the presence of CEA, the CuO nanoparticles (CuO NPs) employed as dual-signal response probes would bond to the microplates and be acidolyzed by HCl to release Cu2+, which could replace Zn2+ and In3+ via the CE reaction. After the CE reaction is completed, the photocurrent would switch from a weak anodic photocurrent to a cathode one by using a 635 nm laser as a signal amplifier, while the photothermal signal would be enhanced with 808 nm laser illumination. On the basis of the polarity-switchable PEC strategy, CEA could be accurately detected from 0.1 to 50 ng mL-1 with a limit of detection (LOD) of 48 pg mL-1 (S/N = 3). Moreover, the photothermal assay for CEA detection possesses a linear range from 0.5 to 100 ng mL-1 with a LOD of 0.21 ng mL-1. In addition, the designed sensing platform only relies on devices with portability that are permitted for point-of-care detection.

Bismuth, Nitrogen-Codoped Carbon Dots as a Dual-Read Optical Sensing Platform for Highly Sensitive, Ultrarapid, Ratiometric Detection of Doxorubicin

Doxorubicin (DOX) is a potent anticancer drug, but it has side effects on normal tissues, particularly myocardial cells. Therefore, it is crucial to detect the DOX concentration in body fluids for effective clinical treatment. In this work, N,Bi-codoped CDs (Bi,N-CDs) were synthesized through a one-step hydrothermal method to carbonize the raw materials of 2,4-dinitroaniline and bismuth nitrate. The resulting Bi,N-CDs showed a reduced emission at 490 nm and an enhanced emission at 590 nm in the presence of DOX. The ratio of fluorescence (FL) intensity (F590/F490) was found to be a reliable indicator of DOX concentration, ranging from 0.05 to 30 μM and 40-200 μM, with detection limits (LOD) of 34 and 24 nM, respectively. A ratiometric fluorescence nanoprobe was established for highly selective and sensitive detection of DOX using a specific electrostatic interaction and inner filter effect between Bi,N-CDs and DOX. Meanwhile, Bi,N-CDs exhibited a distinct color change ranging from yellow to orange-red when exposed to DOX, allowing for a colorimetric method to measure DOX levels in the range of 0.05-30 μM, with a detection limit of 169 nM. The probe was triumphantly used to monitor DOX in actual samples via a dual-mode optical sensing strategy. This study contributes to the development of heteroatom-doped CDs and expands their potential applications for detecting biological samples.

Dual-Modal Bimetallic Nanozyme-Based Sensing Platform Combining Colorimetric and Photothermal Signal Cascade Catalytic Enhancement for Detection of Hypoxanthine to Judge Meat Freshness

Considering the enormous demand for meat in people's daily lives, the development of efficient meat freshness assays is of great significance for safeguarding food safety. Here, a novel bimetallic nanozyme Fe@CeO2 with high peroxidase-like activity was first synthesized by embedding ferrocenecarboxylic acid (Fc) into hollow CeO2 nanospheres, which combined with xanthine oxidase (XOD) to develop a self-supplying H2O2-facilitated enzymatic cascade catalytic system of XOD + Fe@CeO2, yielding a meat freshness indicator hypoxanthine (Hx)-responsive colorimetric and photothermal dual-mode analytical platform for judging meat freshness upon the assistance of 3,3',5,5'-tetramethylbenzidine (TMB). Owing to the catalytic activity of XOD to convert Hx into H2O2, Fe@CeO2 rapidly dissociated it into •OH via a peroxidase activity-triggered Fenton-like reaction, emerging a typical enzymatic cascade catalytic reaction. As a result, the colorless TMB was oxidized to be the product of dark-blue oxTMB by •OH, with a chromogenic reaction-driven absorption enhancement at 652 nm, which endowed it with a significant photothermal effect under 660 nm laser irradiation. On this basis, an Hx concentration-dependent colorimetric and photothermal dual-mode signal cascade catalytic enhancement sensing platform was proposed by integrating with a Color Picker App-installed smartphone and a 660 nm laser-equipped handheld thermal imager, achieving the onsite quantitative, reliable, and visual detection of Hx in real meat samples for judging meat freshness with acceptable results. Notably, the colorimetric and photothermal dual-mode signal cascade catalytic enhancement improved not only the reliability but also the sensitivity of the assay, which provided new insights for efficient onsite visual monitoring of meat freshness to safeguard food safety.

Development of a highly sensitive immunoassay based on pentameric nanobodies for carcinoembryonic antigen detection

BACKGROUND

Carcinoembryonic antigen-related cell adhesion molecule 5 (CEACAM-5) is a well-characterized biomarker for the clinical diagnosis of various cancers. Nanobodies, considered the smallest antibody fragments with intact antigen-binding capacity, have gained significant attention in disease diagnosis and therapy. Due to their peculiar properties, nanobodies have become promising alternative diagnostic reagents in immunoassay. However, nanobodies-based immunoassay is still hindered by small molecular size and low antigen capture efficacy. Therefore, there is a pressing need to develop novel nanobody-based immunoassays with superior performance.

RESULTS

A novel pentameric nanobodies-based immunoassay (PNIA) was developed with enhanced sensitivity and specificity for CEACAM-5 detection. The binding epitopes of three anti-CEACAM-5 nanobodies (Nb1, Nb2 and Nb3) were analyzed. To enhance the capture and detection efficacy of CEACAM-5 in the immunoassay, we engineered bispecific nanobodies (Nb1-Nb2-rFc) as the capture antibody, and developed the FITC-labeled pentameric nanobodies (Nb3-VT1B) as the detection antibody. The binding affinities of Nb1-Nb2-rFc (1.746 × 10-10) and Nb3-VT1B (1.279 × 10-11) were significantly higher than those of unmodified nanobodies (Nb1-rFc, 4.063 × 10-9; Nb2-rFc, 2.136 × 10-8; Nb3, 3.357 × 10-9). The PNIA showed a linear range of 0.625-160 ng mL-1 with a correlation coefficient R2 of 0.9985, and a limit of detection of 0.52 ng mL-1, which was 24-fold lower than the immunoassay using monomeric nanobody. The PNIA was validated with the spiked human serum. The average recoveries ranged from 91.8% to 102% and the coefficients of variation ranged from 0.026% to 0.082%.

SIGNIFICANCE AND NOVELTY

The advantages of nanobodies offer a promising alternative to conventional antibodies in disease diagnosis. The novel PNIA demonstrated superior sensitivity and high specificity for the detection of CEACAM-5 antigen. This bispecific or multivalent nanobody design will provide some new insights into the design of immunoassays for clinical diagnosis.

MnOx In Situ Growth-Induced Luminescence and Oxidase-Like Feature Bimodulation of CePO4:Tb Nanorods: Toward Ascorbic Acid-Related Bioanalysis in a "One-Stone-Two-Birds" Manner

Nanozyme-based multimode detection is a useful means to improve the accuracy and stability of analytical methods. However, both multifunctional nanozymes and related multimodal sensing strategies are still very scarce. Besides, they require complex processes to fabricate and operate. To fill this gap, here we propose a spontaneous interfacial in situ growth strategy to prepare a new bifunctional material (CePO4:Tb@MnOx) featuring good oxidase-like activity and green photoluminescence for the dual-mode colorimetric/luminescence determination of ascorbic acid (AA)-related biomarkers specifically. CePO4:Tb@MnOx was gained through the controllable redox reaction between KMnO4 and CePO4:Tb nanorods. It was interestingly found that MnOx in situ growth not only significantly enhanced the enzyme-like activity but also could reversibly regulate the luminescence of CePO4:Tb via a dual quenching mechanism. More interestingly, CePO4:Tb@MnOx exhibited a distinctive response toward AA against other reducing species. A double-coordination regulation mechanism was further verified to clarify the catalytic activity and luminescence switching behaviors in CePO4:Tb@MnOx. Based on these findings, a dual-mode colorimetric/luminescence approach was established for AA sensing in a "one-stone-two-birds" manner, providing excellent selectivity, sensitivity, and practicability. Furthermore, the determination of AA-related biomarkers, including acid phosphatase activity and organophosphorus residue, was also validated by the sensing principle. Our work not only deepens the understanding of the coordinated regulation of the luminescence and enzyme-like features in lanthanide-based materials but also offers a novel way to design and develop multifunctional nanozymes for advanced bioanalytical applications.

Integrated Design of a Dual-Mode Colorimetric Sensor Driven by Enzyme-like Activity Regulation Strategy for Ultratrace and Portable Detection of Hg2

Colorimetric analysis for mercury detection has great application potential in the prevention of health damage caused by mercury in the environment. Sensitivity, selectivity, and portability are core competencies of sensors, and concentrating these properties in a single sensor for efficient mercury detection remains a great challenge. Herein, a hollow structure CuS@CuSe@PVP (CCP) was prepared in which the enzyme-like activities could be activated by Hg2+ due to the antagonism between Hg and Se, inspiring the establishment of a colorimetric method for Hg2+ detection. As for Hg2+ detection performance, the linear range (LR) and limit of detection (LOD) were 1-900 and 0.81 nM in the POD-like activity system, respectively. Also, 5-550 nM of LR and 2.34 nM of LOD were achieved in the OD-like activity system. Further, a smartphone-mediated portable RGB nanosensor was fabricated, with a LOD down to 6.65 nM in the POD-like system and 7.97 nM in the OD-like system. Moreover, the excellent self-calibration and satisfactory recovery of 94.77%-106.16% were shown in the application of real water samples analysis. This study represented advanced progress toward emerging applications of nanozymes with multiple enzyme-like activities in heavy metal detection and will accelerate the development of efficient and portable heavy metal sensors.

Hollow porphyrin-based porous organic polymer with dual enzyme-like activities for ultra-fast colorimetric detection of Cr (VI) in wastewater

A hollow porphyrin-based porous organic polymer (H-Fe-POP) was prepared for rapid and sensitive colorimetric determination of Cr(VI), which exhibited excellent dual enzyme-like activities, including oxidase-like and peroxidase-like activities. Due to the specific binding of 8-hydroxyquinoline (8-HQ) to Cr(VI), 3,3',5,5'-tetramethylbenzidine (TMB) was liberated, and TMB was oxidized to blue ox-TMB catalyzed by H-Fe-POP. Based on the excellent oxidase-like activity of H-Fe-POP, an ultra-fast colorimetric platform for the detection of Cr(VI) was constructed, allowing the quantification of Cr(VI) in the range 2-130 μM within 30 s with a detection limit of 0.23 μM. Importantly, the sensor can accurately determine Cr(VI) in industrial wastewater, indicating its high potential for environmental monitoring.

Rapid Testing of Δ9-Tetrahydrocannabinol and Its Metabolite On-Site Using a Label-Free Ratiometric Fluorescence Assay on a Smartphone

Excessive consumption of Δ9-tetrahydrocannabinol (THC) severely endangers human health and has raised public safety concerns. However, its quantification by readily rapid tools with simplicity and low cost is still challenging. Herein, we found that a G-rich THC aptamer (THC1.2) can tightly bind to thioflavin T (ThT) with strong fluorescence, which would be specifically quenched in the presence of THC. Based on that, a label-free ratiometric fluorescent sensor for the sensing of THC and its metabolite (THC-COOH) based on THC1.2/ThT as a color emitter and red CdTe quantum dots as reference fluorescence was constructed. Notably, a transition of the fluorescent color of the ratiometric probe from green to red can be instantly observed upon the increased concentration of THC and THC-COOH. Furthermore, a portable smartphone-based fluorescence device integrated with a self-programmed Python program was fabricated and used to accomplish on-site monitoring of THC and THC-COOH within 5 min. Under optimized conditions, this ratiometric fluorescent sensor allowed for an instant response toward THC and its metabolite with considerable limits of detection of 97 and 254 nM, respectively. The established sensor has been successfully applied to urine and saliva samples and exhibited satisfactory recoveries (88-116%). This ratiometric fluorescent sensor can be used for the simultaneous detection of THC and THC-COOH with the advantages of rapidness, low cost, ease of operation, and portability, providing a promising strategy for on-site detection and facilitating law enforcement regulation and roadside control of THC.