Ratiometric fluorescent detection system based on dual-driving catalysis of CuO nanozyme with a classical univariate calibration for the determination of ascorbic acid in serum and fruits

Lanthanide coordination polymers@CuO nanoparticles: Enhanced self-cascade nanoenzyme activity and ratiometric fluorescence assay of glutathione

Tandem enzyme can catalyze some cascade reactions with high efficiency, and some few tandem enzyme-like mimics have been discovered recently. Further improving the catalytic efficiency of tandem nanoenzymes with facile method may undoubtedly promote and broaden their applications in various fields. In this work, cupric oxide nanoparticles (CuO NPs) with dual-functional enzyme mimics were synthesized using the rapid deposition method in advance, which simultaneously combined with lanthanide infinite coordination polymers (Ln ICPs) during the self-assemble of Tb3+, guanine-5'-triphosphate (GTP) and auxiliary ligand terephthalic acid (TA). Excitingly, the obtained Tb-GTP/TA@CuO ICPs, not only displayed obviously enhanced tandem catalytic activity compared with pure CuO NPs, but also provided a versatile ratiometric platform for ultrahigh selective and sensitive detection of glutathione (GSH) under single-wavelength excitation. A good linear relationship between the ratio signal and the GSH concentration was spanning from 0.001 to 20 μM with an impressive detection limit of 0.50 nM. This study opens a new and universal avenue for preparing integrated multifunctional probes by coupling of nanoenzyme catalytic activity with superior luminescent Ln ICPs through facile method.

Ultrarobust stable ABTS radical cation prepared using Spore@Cu-TMA biocomposites for antioxidant capacity assay

Herein, spore@Cu-trimesic acid (TMA) biocomposites were prepared by self-assembling Cu-based metal-organic framework on the surface of Bacillus velezensis spores. The laccase-like activity of spore@Cu-TMA biocomposites was enhanced by 14.9 times compared with that of pure spores due to the reaction of Cu2+ ions with laccase on the spore surface and the microporous structure of Cu-TMA shell promoting material transport and increasing substrate accessibility. Spore@Cu-TMA rapidly oxidized and transformed 2,2'-azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) into ABTS●+ without using H2O2. Under optimum conditions, the ABTS●+ could be stored for 21 days at 4 °C and 7 days at 37 °C without the addition of any stabilizers, allowing for the large-scale preparation and long-term storage of ABTS●+. The ultrarobust stable ABTS●+ obtained with the use of Cu-TMA could effectively reduce the "back reaction" by preventing the leaching of the metabolites released by the spores. On the basis of these findings, a rapid, low-cost, and eco-friendly colorimetric platform was successfully developed for the detection of antioxidant capacity. Determination of antioxidant capacity for several antioxidants such as caffeic acid, glutathione, and Trolox revealed their corresponding limits of detection at 4.83, 8.89, and 7.39 nM, respectively, with linear ranges of 0.01-130, 0.01-140, and 0.01-180 μM, respectively. This study provides a facile way to prepare ultrarobust stable ABTS●+ and presents a potential application of spore@Cu-TMA biocomposites in food detection and bioanalysis.

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.

Recent advances in metal oxide nanozyme-based optical biosensors for food safety assays

Metal oxide nanozymes are emerging as promising materials for food safety detection, offering several advantages over natural enzymes, including superior stability, cost-effectiveness, large-scale production capability, customisable functionality, design options, and ease of modification. Optical biosensors based on metal oxide nanozymes have significantly accelerated the advancement of analytical research, facilitating the rapid, effortless, efficient, and precise detection and characterisation of contaminants in food. However, few reviews have focused on the application of optical biosensors based on metal oxide nanozymes for food safety detection. In this review, the catalytic mechanisms of the catalase, oxidase, peroxidase, and superoxide dismutase activities of metal oxide nanozymes are characterized. Research developments in optical biosensors based on metal oxide nanozymes, including colorimetric, fluorescent, chemiluminescent, and surface-enhanced Raman scattering biosensors, are comprehensively summarized. The application of metal oxide nanozyme-based biosensors for the detection of nitrites, sulphites, metal ions, pesticides, antibiotics, antioxidants, foodborne pathogens, toxins, and other food contaminants has been highlighted. Furthermore, the challenges and future development prospects of metal oxide nanozymes for sensing applications are discussed. This review offers insights and inspiration for further investigations on optical biosensors based on metal oxide nanozymes for food safety detection.

A fluorescent dual-emitting platform for fluorescent "turn-on" ratiometric detection of ascorbic acid in beverages utilizing luminol-embedded iron-based metal-organic frameworks

A fluorescent dual-emitting platform for fluorescent "turn-on" ratiometric detection of ascorbic acid in beverages was developed utilizing luminol-embedded iron-based metal-organic frameworks (luminol@Fe-DOBDC MOFs). Luminol@Fe-DOBDC MOFs with fluorescent emissions at 430 nm and 540 nm under excitation wavelength of 365 nm were applied to detect ascorbic acid on the basis of ascorbic acid triggering the reduction of Fe3+ into Fe2+. In the presence of ascorbic acid, fluorescent intensity at 540 nm was increased significantly while fluorescent intensity at 430 nm was changed slightly. Two emission peaks separated by 110 nm can eliminate environmental interferences by built-in self-calibration of ratiometric signal, enhancing the sensitivity and accuracy. The increasing ratiometric fluorescent intensity (I540 nm/I430 nm) has linear relationship with the concentration of ascorbic acid from 0.2 to 30 μM with limit of detection of 70 nM. It is an efficient, sensitive and accurate platform to detect ascorbic acid in commercial beverages using transition-metal-based MOFs.

The construction of dual-emissive ratiometric fluorescent probes based on fluorescent nanoparticles for the detection of metal ions and small molecules

With the rapid development of fluorescent nanoparticles (FNPs), such as CDs, QDs, and MOFs, the construction of FNP-based probes has played a key role in improving chemical sensors. Ratiometric fluorescent probes exhibit distinct advantages, such as resistance to environmental interference and achieving visualization. Thus, FNP-based dual-emission ratiometric fluorescent probes (DRFPs) have rapidly developed in the field of metal ion and small molecule detection in the past few years. In this review, firstly we introduce the fluorescence sensing mechanisms; then, we focus on the strategies for the fabrication of DRFPs, including hybrid FNPs, single FNPs with intrinsic dual emission and target-induced new emission, and DRFPs based on auxiliary nanoparticles. In the section on hybrid FNPs, methods to assemble two types of FNPs, such as chemical bonding, electrostatic interaction, core satellite or core-shell structures, coordination, and encapsulation, are introduced. In the section on single FNPs with intrinsic dual emission, methods for the design of dual-emission CDs, QDs, and MOFs are discussed. Regarding target-induced new emission, sensitization, coordination, hydrogen bonding, and chemical reaction induced new emissions are discussed. Furthermore, in the section on DRFPs based on auxiliary nanoparticles, auxiliary nanomaterials with the inner filter effect and enzyme mimicking activity are discussed. Finally, the existing challenges and an outlook on the future of DRFP are presented. We sincerely hope that this review will contribute to the quick understanding and exploration of DRFPs by researchers.

Amphiphilic Polymer Capped Perovskite Compositing with Nano Zr-MOF for Nanozyme-Involved Biomimetic Cascade Catalysis

CsPbX3 perovskite nanocrystal (NC) is considered as an excellent optical material and is widely applied in optoelectronics. However, its poor water stability impedes its study in enzyme-like activity, and further inhibits its application in biomimetic cascade catalysis. Herein, for the first time, the oxidase-like and ascorbate oxidase-like activities of an amphiphilic polymer capped CsPbX3 are demonstrated, and its catalytic mechanism is further explored. Furthermore, an all-nanozyme cascade system (multifunctional CsPbBr3 @Zr-metal organic framework (Zr-MOF) and Prussian blue as oxidase-like and peroxidase-like nanozyme) is constructed with a portable paper-based device for realizing the dual-mode (ratiometric fluorescence and colorimetric) detection of ascorbic acid in a point-of-care (POC) fashion. This is the first report on the utilization of all-inorganic CsPbX3 perovskite NC in biomimetic cascade catalysis, which opens a new avenue for POC clinical disease diagnosis.

Colorimetric immunosensing using liposome encapsulated MnO2 nanozymes for SARS-CoV-2 antigen detection

Development of specific signal reporters with signal amplification effect are highly needed for sensitive and accurate detection of pathogen. Herein, we design a colorimetric immunosensing nanosystem based on liposome encapsulated quantum dots-sized MnO2 nanozyme (MnO2QDs@Lip) as a signal reporter for ultrasensitive and fast detection of SARS-CoV-2 antigen. The pathogenic antigens captured and separated by antibody-conjugated magnetic beads (MBs) are further connected with antibody-modified MnO2QDs@Lip to form a sandwich-like immunocomplex structure. After triggered release, MnO2 QDs efficiently catalyze colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue oxidized TMB, which can be qualitatively observed by naked eyes and quantitatively analyzed by UV-Vis spectra or smartphone platforms. By taking advantages of immuno-magnetic separation, excellent peroxidase-like catalytic activity of MnO2 QDs, and high encapsulation efficiency of MnO2QDs@Lip, ultrasensitive detection of SARS-CoV-2 antigen ranging from 0.1 pg/mL to 100 ng/mL is achieved within 20 min. The limit of detection (LOD) is calculated to be 65 fg/mL in PBS buffer. Furthermore, real clinical samples of SARS-CoV-2 antigens can be effectively identified by this immunosensing nanosystem with excellent accuracy. This proposed detection nanosystem provides a strategy for simple, rapid and ultrasensitive detection of pathogens and may shed light on the development of new POCT detection platforms for early diagnosis of pathogens and surveillance in public health.

A Novel Molecularly Imprinted Sensor Based on CuO Nanoparticles with Peroxidase-like Activity for the Selective Determination of Astragaloside-IV

In this work, dopamine (DA) was polymerized on the surface of CuO nanoparticles (CuO NPs) to form a molecularly imprinted polymer (MIP@PDA/CuO NPs) for the colorimetric detection of astragaloside-IV (AS-IV). The synthesis process of MIP is simple and easy to operate, without adding other monomers or initiators. CuO NPs has high peroxidase (POD)-like activity that can catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to generate oxidized TMB (OxTMB) in the presence of H2O2, having a maximum ultraviolet-visible (UV-Vis) absorption peak at 652 nm. The AS-IV can specifically bind to the surface imprinted cavities and prevent the entry of TMB and H2O2, which will lead to the inhibition of the catalytic reaction. Therefore, a new approach based on the POD-like activity of MIP@PDA/CuO NPs for AS-IV detection was developed with a linear range from 0.000341 to 1.024 mg/mL. The LOD and LOQ are 0.000991 and 0.000341 mg/mL, respectively. The developed method can accurately determine AS-IV in Huangqi Granules and different batches of Ganweikang Tablets, which are similar to the results measured by HPLC-ELSD and meet the requirements of Chinese Pharmacopoeia (2020 edition) for the amount of AS-IV in Huangqi Granules. The combination of MIP with CuO NPs not only endows the detection of AS-IV with high selectivity and reliability, but also expands the application of nanozymes in the detection of small-molecule compounds that have weak UV absorption, and do not have reducibility or oxidation properties.

Rapid and sensitive detection of alkaline phosphatase and glucose oxidase activity through fluorescence and colorimetric dual-mode analysis based on CuO NPs@ZIF-8 mediated enzyme-cascade reactions

The combined application of nanozymes and natural enzymes has received widespread attention in recent years. In this work, a simple and efficient method was used to synthesize a composite material of CuO nanoparticle-modified zeolitic imidazolate framework-8 (CuO NPs@ZIF-8) with multiple enzyme activities (glucose oxidase-like and hydrolase-like activities) to detect the activity of natural enzymes through fluorescence and colorimetric (UV-vis) dual-mode detection. The hydrolase- and oxidase-like activities of CuO NPs@ZIF-8 show an acceptable affinity with l-ascorbic acid 2-phosphate trisodium (AAP) and o-phenylenediamine (OPD). Using the developed sensor, highly sensitive detection of natural enzymes glucose oxidase (GOX) and alkaline phosphatase (ALP) was achieved through both fluorescent and colorimetric analyses with a wide linear range (fluorescence for GOX: 0.86-1.23 × 105 mU mL-1, UV-vis for GOX: 0.081-1.62 × 105 mU mL-1; fluorescence for ALP: 0.042-1.20 × 104 mU mL-1, UV-vis for ALP: 0.0046-1.23 × 104 mU mL-1) and low LOQs (fluorescence for GOX: 0.86 mU mL-1, UV-vis for GOX: 0.081 mU mL-1; fluorescence for ALP: 0.042 mU mL-1, UV-vis for ALP: 0.0046 mU mL-1). Compared to the other fluorescent and colorimetric sensors, this sensor has better catalytic activity due to the addition of GOX and ALP, which can amplify the detection signal and improve the sensitivity. This is the first time that composite material CuO NPs@ZIF-8 with "tandem enzyme" activity was synthesized and applied in the detection of enzyme activity. Additionally, the proposed fluorescent and UV-vis platforms exhibit the capability to detect GOX and ALP in serum samples with satisfactory recovery, indicating potential application prospects in biochemical analysis.

A Comprehensive Study: Traditional and Cutting-Edge Analytical Techniques for the Biomarker Based Detection of the Micronutrients & POC Sensing Directions for Next-Generation Diagnostic

Micronutrient deficiency is wide spread and highly affects morbidity, mortality, and well-being of human beings. Micronutrient deficiency gradually manifests into diseases, which effects pathophysiology directly or indirectly. There is an imprecision in the diagnosis of micronutrient deficiency because of two causes; the selection of the standard biomarker and the diagnostic technique used. In appropriate diagnosis could increase the severity of the disorder. Instead of a single a combination of biomarkers can give more stringent results for micronutrient testing. Several traditional analytical techniques are used for diagnosis but HPLC, ELISA & LCMS/MS are most sensitive and reliable methods used by CLSIA-certified labs. However, these techniques require well-equipped, centralized laboratory facilities. The diagnostic era moves toward the Point of Care Testing (POCT), a boon in emerging diagnostics, breaking all paradigms of traditional analytical techniques. POCT led us toward the development of biosensors, which encompasses many techniques like paper-based sensors, microfluidic chip, wearable devices, and smartphone-assisted diagnostics, which become more popular diagnostic tools. This outlook summarizes the micronutrients like vitamins A, B5, B6, B7, B9, B12 C, D, and E and Minerals like iron, calcium, zinc, magnesium, and sodium; along with its biomarkers, analytical techniques, and point of care innovation in micronutrients.

Cerium/polyacrylic acid modified porphyrin metal-organic framework as fluorescence and photothermal sensor for ascorbic acid measurement

A fluorescence and photothermal dual-signal assay was developed for the determination of ascorbic acid (AA). Cerium/polyacrylic acid modified porphyrin metal-organic frameworks (PCN-224@PAA-Ce MOFs) exhibit oxidase-like activity and can effectively oxidize 3,3 ', 5,5 '-tetramethylbenzidine (TMB) from colorless substrates to blue substrates (oxTMB). The absorption spectrum of oxTMB overlaps with the emission spectrum of PCN-224@PAA-Ce, resulting in quenching of fluorescence emission of PCN-224@PAA-Ce. oxTMB, as an excellent photothermal agent, converts the optical signal into the thermal signal (temperature increasing) driven by 808 nm laser. In the presence of AA, the blue oxTMB was reduced to colorless TMB, which led to the fluorescence recovery of PCN-224@PAA-Ce and at the same time, the photothermal signal was changed with the temperature decreasing under the driving of 808 nm laser. The detection limits (LOD) of fluorescence/photothermal dual-mode AA sensor strategies were as low as 0.73 μM and 1.4 μM, respectively. Rapid analysis of ascorbic acid was accomplished with the present procedure, AA in vitamin C tablets and human serum samples were validated.

Modulation of inner filter effect between persistent luminescent particles and 2, 3-diaminophenazine for ratiometric fluorescent assay of ascorbic acid and ascorbate oxidase activity

Ascorbate oxidase (AAO) and ascorbic acid (AA) play an important role in delaying lives senescence and metabolism. In this study, a sensitive ratiometric fluorescence sensing system based on the inner filter effect (IFE) between persistent luminescent particles (PLPs) and 2, 3-diaminophenazine (DAP), was designed for the detection of AA and AAO activity. Wherein, PLPs emit blue fluorescence at 475 nm with an excitation wavelength of 370 nm. CoOOH nanosheets with oxidase-like activity can oxidize o-phenylenediamine (OPD) to produce 2, 3-diaminophenazine (DAP) with orange fluorescence at 558 nm. The generated DAP quenched the fluorescence of PLPs by an inner filter effect (IFE). When AA was introduced to the system, CoOOH nanosheets were destroyed and reduced to Co²⁺, thereby inhibiting the oxidization of OPD and effectively preserving the blue fluorescence of PLPs at 475 nm. Besides, AAO can catalyse AA to produce the oxided dehydroascorbic acid (DHA). The dissipative AA can recover orange fluorescence of DAP with weakening the blue fluorescence of PLPs. Therefore, a sensitive ratio fluorescence sensing strategy was established by using PLPs as the reference signal and DAP as a reported signal for the detection of AA and AAO activity. Under optimal conditions, the obtained linear ranges were 1-45 μM and 1-20 mU/mL, and detection limits were 0.2 μM and 0.25 mU/mL, respectively. Finally, this proposed ratiometric fluorescent analytical strategy was used to detect AA in real samples (lemon, orange, tomato), which exhibited satisfactory results comparing with commercial kit.

Nanozyme-encoded luminescent detection for food safety analysis: An overview of mechanisms and recent applications

With the rapid growth in global food production, delivery, and consumption, reformative food analytical techniques are required to satisfy the monitoring requirements of speed and high sensitivity. Nanozyme-encoded luminescent detections (NLDs) integrating nanozyme-based rapid detections with luminescent output signals have emerged as powerful methods for food safety monitoring, not only because of their preeminent performance in analysis, such as rapid, facile, low background signal, and ultrasensitive, but also due to their strong attractiveness for future sensing research. However, the lack of a full understanding of the fundamentals of NLDs for food safety detection technologies limits their further application. In this review, a systematic overview of the mechanisms of NLDs and their applications in the food industry is summarized, which covers the nanozyme-mimicking types and their luminescent signal generation mechanisms, as well as their applications in monitoring common foodborne contaminants. As demonstrated by previous studies, NLDs are bridging the gap to practical-oriented food analytical technologies and various opportunities to improve their food analytical performance to be considered in the future are proposed.

Lighting Up Agricultural Sustainability in the New Era through Nanozymology: An Overview of Classifications and Their Agricultural Applications

With the concept of sustainable agriculture receiving increasing attention from humankind, nanozymes, nanomaterials with enzyme-like activity but higher environmental endurance and longer-term stability than natural enzymes, have enabled agricultural technologies to be reformative, economic, and portable. Benefiting from their multiple catalytic activities and renewable nanocharacteristics, nanozymes can shine in agricultural scenarios using enzyme engineering and nanoscience, acting as sustainable toolboxes to improve agricultural production and reduce the risk to agricultural systems. Herein, we comprehensively discuss the classifications of nanozymes applied in current agriculture, including peroxidase-like, oxidase-like, catalase-like, superoxide dismutase-like, and laccase-like nanozymes, as well as their biocatalytic mechanisms. Especially, different applications of nanozymes in agriculture are deeply reviewed, covering crop protection and nutrition, agroenvironmental remediation and monitoring, and agroproduct quality monitoring. Finally, the challenges faced by nanozymes in agricultural applications are proposed, and we expect that our review can further enhance agricultural sustainability through nanozymology.

“Motile-targeting” drug delivery platforms based on micro/nanorobots for tumor therapy

Traditional drug delivery systems opened the gate for tumor-targeted therapy, but they generally took advantage of enhanced permeability and retention or ligand-receptor mediated interaction, and thus suffered from limited recognition range (<0.5 nm) and low targeting efficiency (0.7%, median). Alternatively, micro/nanorobots (MNRs) may act as emerging “motile-targeting” drug delivery platforms to deliver therapeutic payloads, thereby making a giant step toward effective and safe cancer treatment due to their autonomous movement and navigation in biological media. This review focuses on the most recent developments of MNRs in “motile-targeting” drug delivery. After a brief introduction to traditional tumor-targeted drug delivery strategies and various MNRs, the representative applications of MNRs in “motile-targeting” drug delivery are systematically streamlined in terms of the propelling mechanisms. Following a discussion of the current challenges of each type of MNR in biomedical applications, as well as future prospects, several promising designs for MNRs that could benefit in “motile-targeting” drug delivery are proposed. This work is expected to attract and motivate researchers from different communities to advance the creation and practical application of the “motile-targeting” drug delivery platforms.

Peroxidase-like activity of bimetal Cu-Zn oxide mesoporous nanospheres for the determination of o-aminophenol

To enhance the peroxidase-like performance and its application in detection of toxic o-aminophenol (o-AP), a kind of bimetal Cu-Zn oxide-based mesoporous nanosphere (Cu_2/3Zn_1/3O PNPs) was constructed under microwave-radiation conditions. Its mesoporous microstructure and peroxidase-like catalytic activity were investigated in detail. The results showed that Cu_2/3Zn_1/3O PNPs possessed a high specific surface area of 34.89 m²g^-1 and a well-distributed mesoporous size of approximate 6.07 nm, which endowed the superior peroxidase-like performance. The material catalyzes the oxidization of 3,3',5,5'-tetramethylbenzidine (TMB) with K_m/V_max of 0.104 mM/3.79 × 10^-8 M·s^-1 in the presence of H₂O₂. Especially o-AP could exclusively deteriorate the characteristic UV-Vis absorbance intensity at 653 nm (A₆₅₃) of the Cu_2/3Zn_1/3O PNPs-TMB-H₂O₂ system with obvious color change from blue to colorless. Under the optimal conditions, the effect of some interfering substances was low and the limit of detection (LOD) for o-AP was 1.65 × 10^-8 mol/L (S/N = 3). When applied to the colorimetric detection of o-AP in practice, the recovery was between 96.1 and 107.2% with R.S.D. less than 2.04%. The mechanism of synergic-enhancement peroxidase-mimic activity of Cu_2/3Zn_1/3O PNPs and its exclusive colorimetric response to o-AP were proposed as well.

Construction of a ratiometric fluorescence sensing platform based on DES-CDs/CoOOH/OPD system for ascorbic acid detection

Herein, a ratiometric fluorescence sensing platform based on deep eutectic solvent-carbon dots (DES-CDs) was constructed to efficiently determine ascorbic acid (AA). The CDs were synthesized by hydrothermal method using green...