The electrochemical reduction of CO2 into value-added chemicals has been explored as a promising solution to realize carbon neutrality and inhibit global warming. This involves utilizing the electrochemical CO2 reduction reaction (CO2RR) to produce a variety of single-carbon (C-1) and multi-carbon (C2+) products. Additionally, the electrolyte solution in the CO2RR system can be enriched with nitrogen sources (such as NO3-, NO2-, N-2, or NO) to enable the synthesis of organonitrogen compounds via C-N coupling reactions. However, the electrochemical conversion of CO2 into valuable chemicals still faces challenges in terms of low product yield, poor faradaic efficiency (FE), and unclear understanding of the reaction mechanism. This review summarizes the promising strategies aimed at achieving selective production of diverse carbon-containing products, including CO, formate, hydrocarbons, alcohols, and organonitrogen compounds. These approaches involve the rational design of electrocatalysts and the construction of coupled electrocatalytic reaction systems. Moreover, this review presents the underlying reaction mechanisms, identifies the existing challenges, and highlights the prospects of the electrosynthesis processes. The aim is to offer valuable insights and guidance for future research on the electrocatalytic conversion of CO2 into carbon-containing products of enhanced value-added potential.

The identification and quantification of melatonin (MT) are crucial for early diagnosis of disorders associated with circadian rhythm disruption. Herein, novel blue-emissive carbon dots (BCDs) were synthesized through an improved hydrothermal treatment using serine and malic acid as reductant and carbon source. The excellent optical properties of the as-obtained BCDs were used for ratiometric sensing by strategically constructing a MT sensing system integrating BCDs with C3N4 nanosheets loaded with platinum/ruthenium nanoparticles (PtRu/CN). In this system, H2O2 activated the peroxidase-like activity of PtRu/CN to generate •OH and 1O2 for oxidizing the colorless o-phenylenediamine (OPD) into yellow 2,3-diaminophenazine (DAP) with fluorescence emission at 565 nm. Concurrently, the fluorescence emission of BCDs at 439 nm was quenched by the generated DAP via the static quenching and inner filter effect (IFE) process. However, MT rapidly scavenged the generated free radicals to reverse the ratio fluorescence signal. The developed BCDs/PtRu/CN/OPD/H2O2 sensing platform enabled quantitative analysis of MT at concentrations ranging from 0.06 to 600 μmol/L with a low detection limit of 23.56 nmol/L. Moreover, smartphone-based RGB sensing of MT was successfully developed for rapid visualization and portable processing. More broadly, novel insights into the preparation of carbon dots with sensitive fluorescence sensing properties were presented, promising for future considerations.

A novel surface-enhanced Raman scattering (SERS) and catalytic hairpin assembly (CHA) technique dependent dual-signal amplification method for double detection of microRNAs (miRNAs) was created in this work. When target miRNAs were present, CHA reactions could be triggered between the corresponding hairpin DNAs, fixing the SERS tags (two distinct Raman reporters, 4-mercaptobenzonitrile and 4-mercaptopyridine, which were pre-labeled in the space between Au core and silver shell nanoparticles) onto the gold nanoclusters-doped covalent organic frameworks (AuNCs/COF) nanofiber substrate surface, which generated numerous “hot spots” and ultimately produced amplified SERS signals. Besides, with the help of the CHA cycles, much more target miRNAs were captured to improve the detection sensitivity and decrease the detection limit of multiplex detection down to 77 aM for miRNA-21 and 93 aM for miRNA-155, respectively. This SERS biosensor also exhibited a broad detection range (10−16 −10−12 M), good specificity, high reproducibility, as well as excellent recoveries in spiked human serum samples (in the range of 94.5–99.4%). The findings of our experiment suggested that the multiple signal amplification biosensors that were developed have significant potential for multiplex detection of cancer biomarkers (miRNAs and their analogs) in the fields of bioanalysis and clinical biomedicine.

Developing a strong catalytic antifouling membrane to achieve efficient sewage purification has great potential for alleviating water crisis. In this work, we designed and prepared an Fe/Cu-layered double hydroxide (Fe-Cu LDH)-coated polyvinylidene fluoride (PVDF) composite membrane (PVDF/Fe-Cu LDHs) with strong antifouling and activating peroxymonosulfate (PMS) catalytic degradation performance through polydopamine-coordination anchoring and hydrothermal reaction. The results showed that abundant hydroxyl groups of the LDH surface endowed the superhydrophilicity (water contact angle <10 degrees) and underwater superoleophobicity (underwater-oil contact angle >150 degrees) of the membrane surface, which displayed outstanding resistance to crude oil adhesion. With assistance of the LDH surface-bound sulfate radical of the peroxymonosulfate system, the PVDF/Fe-Cu LDH membrane demonstrated robust catalytic degradation performance for the methylene blue (MB) in the dark; the degradation rate constant (k, min(-1)) reached 0.96. Meanwhile, facing the oily wastewater, the selective wettability and charge effect of LDH of the surface made the PVDF/Fe-Cu LDH membrane realize the separation for the various surfactant-free and surfactant-stabilized emulsions. Importantly, the PMS-activation catalytic produced the ROS (center dot SO4-,center dot OH, center dot O-2(-), and O-1(2)), which enhanced the regeneration of the fouled PVDF/Fe-Cu LDH membrane and obtained a high flux recovery ratio in the dark (94.7%) after 10 cycles of separation experiments. Hence, we believed that the PVDF/Fe-Cu LDH membrane can provide inspiration for the development and further practical application of antifouling membranes.

The involvement of microRNA (miRNA) in the transcriptional and regulatory processes of gene expression in organisms, along with its aberrant expression patterns in various malignant diseases such as tumors, underscores its significance. Surface-enhanced Raman scattering (SERS) biosensing technology offers distinct advantages for miRNA detection, including simplified procedures, non-destructive analysis, fingerprint spectroscopy capabilities, and rapid detection times. This study presents the development of a novel SERS-based biosensor utilizing miRNA-21 stimulated-responsive DNA-functionalized nanomaterials. The DNA structure within the the catalyzed hairpin amplification (CHA) was utilized to modify Fe3O4 3 O 4 and Au nanocubes (Au NCs), and subsequently, miRNA21 served as a key to trigger the CHA reaction between these two materials. Notably, during this process, the signal probe Cy3 underwent directed migration and accumulation from Fe3O4 3 O 4 to Au NCs, resulting in the unidirectional enrichment of beacon probe from Fe3O4 3 O 4 to Au NCs, which was facilitated by the progression of the CHA cycle. This facilitated robust generation of SERS signals for precise quantification of miRNA-21. The sensor utilized Au NCs enriched with Cy3 to form highly stable and well-ordered two-dimensional arrays at the watercyclohexane interface, demonstrating exceptional stability and reproducibility. It achieved an impressive detection limit of 0.81 fM across a dynamic range from 1 to 1 x 106 6 fM. This work advances practical methods for amplification analysis in the sensing field, demonstrating significant potential for clinical medicine and early cancer diagnosis.

Highly efficient nanozymes are useful for constructing sensors with exceptional performance. Herein, carbon nanotubes loaded with ruthenium nanoclusters (Ru/CNTs) were successfully prepared through a straightforward ambient chelating reduction synthetic method. The strong d-it interactions between CNTs and metallic Ru facilitated the nucleation, dispersion, and enduring stability of Ru nanoclusters. Benefiting from the robust peroxidase-like activity and recyclability of Ru/CNTs, an accurate colorimetric sensing platform was established for efficient (3-glucosidase (BG) sensing. Ru/CNTs efficiently catalyzed H2O2 2 O 2 to generate reactive oxygen species (ROS, O 2 center dot- and 1 O 2 ), initiating the chromogenic reaction of 3,3 ',5,5 '-tetramethylbenzidine ' ,5,5 '-tetramethylbenzidine (TMB). However, the above chromogenic reaction was suppressed in the presence of HQ due to its inherent reducibility. Using phenolic (3-arbutin (BA) as substrate, BG catalyzed the hydrolysis of BA, releasing HQ. The proposed Ru/CNTsbased sensing system, involving the implementation of two-step catalytic reactions and concurrently possessing the stability and high specificity of enzymes, significantly enhanced the system's selectivity and sensitivity. As expected, this colorimetric sensor exhibited remarkable sensitivity (limit of detection, LOD 0.472 U L- 1 ) with exceptional accuracy (recoveries, 94.84-111.32 %; RSD, 0.89-3.07 %). Overall, the proposed cascade catalysis strategy significantly enhanced the stability and sensitivity of the sensor, paving the way for its practical application in the fields of food and biology.

Chloramphenicol (CAP), as a broad-spectrum antibiotic, is genotoxic to humans. In this paper, a "Y-shaped" SERS biosensor based on magnetic plasmonic superstructures Fe3O4@SiO2@Ag flowers and the highly efficient isothermal amplification strategy of exponential amplification reaction (EXPAR) technology was proposed for ultrasensitive detection of CAP in milk. This was achieved by forming a stable "Y-shaped" structure on the abundant sharp tips of Fe3O4@SiO2@Ag flowers through specific three-part assembly (Probe 1 connected to the magnetic substrate, Signal Probe 2 Au@4-NTP, and the EXPAR amplification product Amplicon). When the CAP was present, the Amplicon obtained from EXPAR amplification could form a "Y-shaped" structure with the magnetic material and the signal probe. Benefiting from the abundant branching, extensive surface area, and rough surface of the magnetic Fe3O4@SiO2@Ag flower, it offers a multitude of "hot spots" for plasmonic coupling in the electromagnetic field gap region and significantly reduces the nanogap between the signal probe and the silver nanoflowers by constructing a "Y"-shaped structure, thereby maximizing the amplification of the Raman signal. Enabling the detection range of CAP to be between 10(-6) and 10(-13) M with a detection limit of 17.9 fM. This strategy provided an avenue for trace detection of CAP in food.

Since the discovery of graphene, its excellent optical, electrical, and mechanical properties have important application prospects in numerous fields. Herein, introducing the related application of graphene into chemical experiments is of great significance to enhance students' extracurricular knowledge and cultivate their scientific research consciousness. In this experiment, we designed a multifunctional GO/TA@beta-FeOOH membrane with a multilayered structure to achieve sewage treatment. The whole experiment teaching includes the preparation, characterization, and application of a graphene oxide (GO)-based membrane, which can enhance undergraduates' practical ability, increase understanding of modern scientific research methods, and inspire scientific research thinking. For the membrane preparation method, the vacuum-assisted methods, polyphenol complex cross-linking reaction, and biomimetic mineralization functionalization would increase students' theoretical knowledge of chemical reactions and processes. Meanwhile, surface structure and composition analysis of modern analytical techniques (SEM, AFM, XPS, and FT-IR) can deepen the students' understanding and application of instrumental analysis. During the performance evaluation process, the newly designed comprehensive experimental teaching not only demonstrates some cross background knowledge of environmental science, material science, separation, and chemical engineering but also provided some basic theories of interfacial wettability, membrane separation engineering for removing oil and dyes, and photo-Fenton catalytic degradation technology for the dyes, which further motivated students' interest in topics of GO-based membrane, enhanced the execution of experimental operations, and depended on their understanding of environmental pollution. Hence, we believe that this novel experimental teaching project is helpful for college students to improve their comprehensive quality, enhancing their innovation and practical ability.

With environmental pollution becoming more serious, developing efficient treatment technologies for all kinds of organic wastewater has become the focus of current research. In this work, the coaxial electrospinning technology was used to one-step fabricate a porous and underwater superoleophobic polyacrylonitrile nanofibrous membrane with an Fe-based metal-organic framework (MIL-100(Fe)). Benefiting from the synergistic effect of two jets, the nanofibers are smaller and denser, which prompt the exposure of more nanomaterial additives (MIL-100(Fe)). The BET surface area increased to 202.888 m2/g, and the membranes demonstrated outstanding underwater superoleophobicity. Moreover, compared with traditional blended matrix membranes by the single-axis method, separation of the modifier and membrane matrix material by coaxial methods also maintained excellent mechanical properties, which enhanced Young's modulus 3.4 times (∼1.34 MPa). As a result, facing soluble dyes, the porous C-PAN/MIL-100(Fe) membrane can demonstrate outstanding and fast adsorptive property (the Qm of MB and CR reached 44.71 and 88.74 mg g-1, respectively). For oily emulsion, the hydrophilic and oleophobic nanofibrous reticular surface provided excellent separation performance (flux: 1124.0-1549.3 L m-2 h-1, R > 98%). Moreover, the porous and underwater superoleophobic C-PAN/MIL-100(Fe)-0.5 membrane can synchronously purify the dye/oil mixture emulsions by one-step filtration. Based on the above performance, we believe that the modified nanofibrous membrane prepared by one-step coaxial electrospinning technology can promote more studies of the development of membrane preparation technology in the field of oily wastewater treatment.

Developing highly-efficient electrocatalysts for the nitrate reduction reaction (NITRR) is a persistent challenge. Here, we present the successful synthesis of 14 amorphous/low crystallinity metal nanofilms on threedimensional carbon fibers (M-NFs/CP), including Al, Ti, Mn, Fe, Co, Ni, Cu, Zn, Ag, In, Sn, Pb, Au, or Bi, using rapid thermal evaporation. Among these samples, our study identifies the amorphous Co nanofilm with fine agglomerated Co clusters as the optimal electrocatalyst for NITRR in a neutral medium. The resulting CoNFs/CP exhibits a remarkable Faradaic efficiency (FENH3) of 91.15 % at - 0.9 V vs RHE, surpassing commercial Co foil (39 %) and Co powder (20 %), despite sharing the same metal composition. Furthermore, during the electrochemical NITRR, the key intermediates on the surface of the Co-NFs/CP catalyst were detected by in situ Fourier-transform infrared (FTIR) spectroscopy, and the possible reaction ways were probed by Density functional theory (DFT) calculations. Theoretical calculations illustrate that the abundant low-coordinate Co atoms of Co-NFs/CP could enhances the adsorption of *NO3 intermediates compared to crystalline Co. Additionally, the amorphous Co structure lowers the energy barrier for the rate-determining step (*NH2 ->*NH3). This work opens a new avenue for the controllable synthesis of amorphous/low crystallinity metal nano-catalysts for various electrocatalysis reaction applications.

The identification and quantification of xanthine are crucial for assessing the freshness and quality of food products, particularly in the seafood industry. Herein, a new approach was developed, involving the in-situ controllable growth of Pt91Ru9 nanoparticles on graphitic carbon nitride to yield Pt91Ru9@C3N4 catalytic materials. By integrating Pt91Ru9@C3N4 with the xanthine/xanthine oxidase (XOD) enzyme catalytic system, a nanozyme-enzyme tandem platform was obtained for the quantification analysis of xanthine. Under the catalytic oxidation of xanthine by XOD in the presence O2, H2O2 was generated. Upon the addition of peroxidase-like activity of Pt91Ru9@C3N4, H2O2 can be decomposed into •OH and 1O2, which can further catalyze the oxidation of TMB to its oxidation product oxTMB with an absorption peak at 652 nm. This smartphone-assisted portable colorimetric sensor for visual monitoring xanthine with a low detection limit of 8.92 nmol L−1, and successfully applied to detect xanthine in grass carp and serum samples.

In this study, a target induced DNAzyme amplifaction strategy was developed combining with peanut-shaped FexOy@macro-/mesoporous carbon (MMC)@Au and covalent organic frameworks (COF)@Au to construct surface enhanced Raman spectrum (SERS) aptasensor for ultrasensitive detection of chloramphenicol (CAP). The polydopamine was firstly self-polymerized on the peanut-shaped Fe2O3 as a reductant to generate a uniform assembly of AuNPs, with multiple hotspots, to achieve high reproducibility. After carbonation process, the obtained magnetic peanut-shaped FexOy@MMC@Au could effectively avoid the Raman interference of the SERS substrate. When target CAP was dropped into the aptamer and DNAzyme double chains, CAP could specifically combining with aptamer, releasing DNAzyme chain to cut off hairpin DNA which was already assembled on the FexOy@MMC@Au. At this time, COF@Au@toluidine blue (TB)@S1 can be attract closed to the SERS substrate due to the complementation of S1 with residual hairpin DNA to produce strong Raman signal. Based on this principle, the SERS aptasensor for the detection of CAP possessed a very low limit of detection (LOD) of 7.35 fM was obtained. The results suggested the potential of this SERS aptasensor for sensitive and selective CAP diagnosis and be applied to the clinical and biochemical analysis.

Herein, an adenosine triphosphate (ATP)-induced enzyme-catalyzed cascade reaction system based on metal-organic framework/alkaline phosphatase (MOF/ALP) nanocomposites was designed to establish a surface-enhanced Raman spectroscopy (SERS) biosensor for use in rapid, sensitive ATP detection. Numerous ALP molecules were first encapsulated using ZIF-90 to temporarily deactivate the enzyme activity, similar to a lock. Au nanostars (AuNSs), as SERS-enhancing substrates, were combined with o-phenylenediamine (OPD) to form AuNSs@OPD, which could significantly improve the Raman signal of OPD. When the target ATP interacted with the MOF/ALP nanocomposites, ATP could act as a key to open the MOF structure, releasing ALP, which should further catalyze the conversion of OPD to oxOPD with the aid of ascorbic acid 2-phosphate. Therefore, with the increasing concentrations of ATP, more ALP was released to catalyze the conversion of OPD, resulting in the reduced intensity of the Raman peak at 1262 cm-1, corresponding to the level of OPD. Based on this principle, the ATP-induced enzyme-catalyzed cascade reaction SERS biosensor enabled the ultrasensitive detection of ATP, with a low detection limit of 0.075 pM. Consequently, this study provides a novel strategy for use in the ultrasensitive, rapid detection of ATP, which displays considerable potential for application in the fields of biomedicine and disease diagnosis.

The electrochemical coreduction of carbon dioxide (CO2) and nitrogenous species (such as NO3-, NO2-, N2, and NO) for urea synthesis under ambient conditions provides a promising solution to realize carbon/nitrogen neutrality and mitigate environmental pollution. Although an increasing number of studies have made some breakthroughs in electrochemical urea synthesis, the unsatisfactory Faradaic efficiency, low urea yield rate, and ambiguous C-N coupling reaction mechanisms remain the major obstacles to its large-scale applications. In this review, we present the recent progress on electrochemical urea synthesis based on CO2 and nitrogenous species in aqueous solutions under ambient conditions, providing useful guidance and discussion on the rational design of metal nanocatalyst, the understanding of the C-N coupling reaction mechanism, and existing challenges and prospects for electrochemical urea synthesis. We hope that this review can stimulate more insights and inspiration toward the development of electrocatalytic urea synthesis technology.

Herein, nitrogen-doped copper nanosheet (CuT@N NS) was obtained by pyrolysis of the tryptophan-based Cucontaining nanosheet (CuT NS) and graphitic carbon nitride (g-C3N4). The high Cu loading (8.62 wt%) on the nitrogen-doped carbon-nanosheets endowed CuT@N NS with prominent peroxidase-mimicking activity. A fluommetric sensing platform comprising CuT@N NS with exceptional catalytic performance and 5-methyl-2-thiouracil capped gold nanoclusters (AuNCs) was successfully constructed for the determination of sarcosine. Under appropriate conditions, sarcosine oxidase (SOx) recognized and oxidized the sarcosine substrate to generate H2O2. The as-obtained CuT@N NS then decomposed H2O2 into superoxide radicals (O-2(center dot-)) and further promoted the reaction between 4-aminoantipyrine (AAP) and phenol to form pink-red quinone-imine dye (p-QID, absorbance at 508 nm). When excited at 380 nm, the orange-emitting AuNCs peak at 560 nm was quenched by the produced p-QID via inner filter effect (IFE). Thus, a CuT@N NS/AuNCs-based fluommetric sensing strategy for sarcosine analysis was constructed. Impressively, the outputting fluorometric signal revealed a wide linear range of 7.5-1100 mu mol L-1 with the detection limit of 4.69 mu mol L-1. These findings not only expanded the applications of nanozyme in bioanalysis, but also provided a sensitive and effective approach for monitoring the levels of sarcosine.

Herein, a ratiometric fluorescent nanoprobe was strategically fabricated using pH-sensitive azamonardine (Aza) as a pH indicator and pH-insensitive AIZS QDs as a reference fluorescence signal for urea activity determination and pH sensing. As the pH changed from 9.7 to 11.7, the resorcinol could react with dopamine to form the cyclization product (Aza), producing a fluorescence signal at 455 nm. Meanwhile, the fluorescence intensity of AIZS QDs at 566 nm remained unchanged. Thus, the ratio of the fluorescence intensity (F-455/F-566) was able to quantify pH value. Our designed pH-sensing platform showed a linear respond to pH values in the range of 9.7 to 11.7 at intervals of 0.2. In addition, the hydrolysis of urea by urease caused an increase of the system pH value, which can be used to measure the concentration of urea. The developed method for urea determination exhibited a good linear relationship from 0.02 to 20 mM and the limit of detection was 0.0103 mM. Moreover, the practical application was confirmed by urea analysis in real water sample with high feasibility and accuracy, indicating the great application prospects of this sensing platform for urea activity analysis.

Making the gold-thiolate shell rigid is an appealing and efficient strategy for improving the fluorescence of gold nanoclusters (GNCs). In this study, ultrabright lysozyme-functionalized 5-methyl-2-thiouracil gold nanoclusters (MT-LZ@GNCs) with yellow emission were rationally designed and synthesized based on MT@GNCs by making the NC shell modified with the lysozyme. The resultant MT-LZ@GNCs exhibited a remarkable luminescence efficiency, high stability, and water-solubility. By combining MT-LZ@GNCs with iron-doped carbon-nanosheet (Fe/C NS) that mimicked peroxidase-like activity, a novel fluorescent nanoprobe was developed for the determination of xanthine. Under the catalysis of xanthine oxidase (XOD), hydrogen peroxide (H2O2) was produced during the oxidation of xanthine. In the presence of H2O2, Fe/C NS can effectively catalyze H2O2 to generate reactive oxygen species (ROS) and subsequently catalyze p-phenylenediamine (PPD) to form its oxidized product (PPDox), thereby quenching the fluorescence of MT-LZ@GNCs at 550 nm via fluorescence resonance energy transfer (FRET). Coupling the peroxidase-like activity of Fe/C NS and XOD cascade reactions, the proposed sensing platform based on MT-LZ@GNCs and Fe/C NS can realize the quantitative analysis of xanthine in the range from 0.5 to 400 mu mot L-1, affording a low detection limit of 0.23 mu mol L-1. In addition, this study provided satisfactory results for monitoring the xanthine content of real samples.

Development and application of carbon-based nanozymes are attracting wide interest in recent years. Abnormal glucose level can be threat to human health. Sensitive and accurate sensing methods for glucose are still of great urgency. In this work, we constructed a sensitive nanozyme-based ratiometric fluorescence sensing platform for glucose. The sensing system composed of copper-doped carbon-based nanozyme (CuAA) with superb peroxidaselike activity and Mg/N doped carbon quantum dots (Mg-N-CQDs) with distinguished fluorescence property. Efficient tandem catalysis of glucose oxidase (Glu Ox) and CuAA, and inner-filter effect (IFE) between 2, 3-diaminophenazine (DAP) and Mg-N-CQDs played crucial roles in this sensing system. The oxidization of glucose was catalyzed by Glu Ox firstly to produce H2O2. In the presence of H2O2, fluorescent DAP was formed from non fluorescent substrate o-phenylenediamine (OPD) with assistance of CuAA, resulting in generation of emission at 558 nm. Meanwhile, the emission at 444 nm from Mg-N-CQDs was quenched efficiently by DAP through IFE. The ratiometric fluorescence signal I558/I444 increased linearly with glucose concentration in the scope of 2-400 mu mol L-1, the limit of detection (LOD) was 1.56 mu mol L-1. It was also practicable to apply the method to the determination of glucose in human serum, satisfactory recoveries and RSDs were acquired.

The synthesis of highly sensitive and selective luminescent probes provides a vital and efficient approach for diagnosing and preventing clinical diseases. In this work, gold-platinum bimetallic nanoclusters (Au - PtNCsGMP) were synthesized with guanosine monophosphate (GMP) as the capping agent, which possessed strong fluorescent emission at 418 nm, and also exhibited great peroxidase-like mimetic activity. Glucose can be catalyzed to generate H2O2 by glucose oxidase, in the presence of H2O2, o-phenylenediamine (OPD) regarded as a representative non-fluorescent substance was catalyzed by Au-PtNCs-GMP and produced fluorescent 2,3-diaminophenazine (DAP) with an emission wavelength of 560 nm. Furthermore, the colorless OPD was oxidized to yellow DAP with UV-vis absorption peak at 420 nm. The generation of DAP can efficiently quench the fluorescence signal of Au-PtNCs-GMP at 418 nm on account of inner filter effect (IFE). The decrease of Au-PtNCsGMP fluorescence and the increase of DAP fluorescence made it possible to detect glucose via ratiometric fluorometric intensity. Thus, a ratiometric fluorescent and colorimetric dual-mode sensing was achieved for glucose detection. The linear ranges of ratiometric fluorescence method and colorimetric method toward glucose were in the range of 0.01-0.4 mM and 0.05-0.4 mM, with the low limits of detection (LOD) of 7 mu M and 11 mu M, respectively. In addition, this dual-mode sensing method can be used for detecting glucose concentration in real biological samples with satisfying results, which provided a valuable and reliable strategy for glucose-related detections.

Developing high-performance nanozyme for the construction of high-sensitivity biosensor platform is of great significance. Herein, we have designed and synthesized a Cu/N co-doped carbon-based nanozyme by anchoring Cu atoms on two-dimensional carbon nanosheet (Cu/NC NS). The Cu/NC NS possessed ultra-high Cu loading, superior peroxidase-like catalytic activity, great stability and reusability. Significantly, the Cu/NC NS exhibited high affinity towards H2O2 and 3,3',5,5'-tetramethylbenzidine (TMB) under acidic condition, which could induce obvious color changes of TMB in the presence of low H2O2 concentration. By integrating the Cu/NC NS with β-galactosidase (β-Gal) and galactose oxidase (Gal Ox), a multienzyme cascade colorimetric sensing system was established for the detection of lactose and β-Gal, which realizing the assay of lactose and β-Gal in the linear ranges of 0.1-1.4 mM and 0.025-0.2 U/mL, respectively. And the limit of detection for lactose and β-Gal were 0.03 mM and 0.01 U/mL, respectively. Furthermore, this work achieved the accurate detection of the content of lactose in milk and the activity of β-Gal in human serum, exploiting a novel application for nanozyme in biosensing.