Nuanfei Zhu

Biomimic nanozymes coassembled by peptides or proteins and small active molecules provide an effective strategy to design attractive nanozymes. Although some promising nanozymes have been reported, rational regulation for higher catalytic activity of biomimic nanozymes remains challenging. Hence, we proposed a novel biomimic nanozyme by encapsulating the coassembly of hemin/bovine serum albumin (BSA) in zeolite imidazolate frameworks (ZIF-8) to achieve controllable tailoring of peroxidase-like activity via the confinement effect. The assembly of Hemin@BSA was inspired by the structure of horseradish peroxidase (HRP), in which hemin served as the active cofactor surrounded by BSA as a blocking pocket to construct a favorable hydrophobic space for substrate enrichment. Benefiting from the confinement effect, ZIF-8 with a porous intracavity was identified as the ideal outer layer for Hemin@BSA to accelerate substrate transport and achieve internal circulation of peroxidase-like catalysis, significantly enhancing its peroxidase-like activity. Especially, the precise encapsulation of Hemin@BSA in ZIF-8 could also prevent it from decomposition in harsh environments by rapid crystallization around Hemin@BSA to form a protective shell. Based on the improved peroxidase-like activity of Hemin@BSA@ZIF-8, several applications were successfully performed for the sensitive detection of small molecules including H2O2, glucose, and bisphenol A (BPA). Satisfactory results highlight that using a ZIF-8 outer layer to encapsulate Hemin@BSA offers a very effective and successful strategy to improve the peroxidase-like activity and the stability of biomimic nanozymes, broadening the potential application of biocatalytic metal–organic frameworks (MOFs).

Herein, a portable lab-in-a-syringe device integrated with a smartphone sensing platform was designed for rapid, visual quantitative determination of organophosphorus pesticides (OPs) via colorimetric and fluorescent signals. The device was chiefly made up of a conjugate pad labeled with cetyltrimethylammonium bromide-coated gold nanoparticles (CTAB-Au NPs) and a sensing pad modified by ratiometric probes (red-emission quantum dots@SiO2 nanoparticles@green-emission quantum dots, rQDs@SiO2@gQDs probe), which was assembled through a disposable syringe and reusable plastic filter. In the detection system, thiocholine (Tch), the hydrolysis product of thioacetylcholine (ATch) by acetylcholinesterase (AchE), could trigger the aggregation of CTAB-Au NPs, resulting in a significant color change from red to purple. Then, CTAB-Au NPs flowed vertically upward and bound to the rQDs@SiO2@gQDs probe on the sensing pad, reducing the fluorescence resonance energy transfer effect between CTAB-Au NPs and gQDs. Meanwhile, rQDs embedded in SiO2 NPs remained stable as internal reference fluorescence, achieving a color transition from red to green. Thus, based on the inhibition of AChE activity by OPs, a colorimetric and fluorescent dual-mode platform was constructed for on-site detection of OPs. Using glyphosate as a model, with the support of a color recognizer application (APP) on a smartphone, the ratio of red and green channel values could be utilized for accurate OP quantitative analysis ranging from 0 to 10 μM with a detection limit of 2.81 nM (recoveries, 90.8–122.4%; CV, 1.2–3.4%). Overall, the portable lab-in-a-syringe device based on a smartphone sensing platform integrated sample monitoring and result analysis in the field, implying great potential for on-site detection of OPs.

The necessary step of directly adding hydrogen peroxide (H2O2) into the detection system in traditional immunoassays hampers their applications as a portable device for point-of-care analysis due to the unstable liquid form of H2O2. Herein, a strategy of self-supplying H2O2 and signal amplification triggering by copper peroxide nanodots encapsulated (CPNs) in metal–organic frameworks (ZIF-8) was proposed in an immunoassay for dual-signal detection of bisphenol A (a typical emerging organic pollutant), which was further fabricated as a lab-in-a-tube device integrated with a smartphone sensing platform. Herein, CPNs@ZIF-8 was modified on the antibody against bisphenol A; after the competitive binding of analytes, coating antigens, and antibodies, the released H2O2 and Cu2+ from encapsulated CPNs under the acidic condition will trigger a Fenton-like reaction to generate ·OH for oxidization of TMB; meanwhile, Cu2+ could quench the fluorescence of GSH-Au NCs, resulting in dual-mode signals for measurements. Most importantly, self-supplying H2O2 with high stability was undertaken by CPNs, and the remarkably increased signal molecule (CPN) loading was ascribed to the excellent capacity of metal–organic frameworks (ZIF-8). In addition, good recoveries were obtained from a colorimetric/fluorescent dual-mode strategy. The constructed device demonstrated great potential as a universal platform for rapid detection of various environmental contaminants using corresponding antibodies relying on its performance of satisfactory stability, sensitivity, and accuracy.

The development of a simple and sensitive method for glucose determination is significant in the early diagnosis and treatment of diabetes. However, current analytical approaches have various defects in their applications. Here, an attractive chemiluminescence-based sensor is developed for one-step and rapid detection of glucose in human urine. In this work, a 2D metal–organic framework (2D-MOF) nanosheet with peroxidase activity was first synthesized, which could catalyze the decomposition of hydrogen peroxide (H2O2) and further oxidize luminol to produce a strong chemiluminescence signal. Then, luminol and glucose oxidase (GOD) were successively labeled on the 2D-MOF nanosheet, obtaining a simple chemiluminescence-functionalized sensor (Co-TCPP(Fe)@luminol@GOD). When Co-TCPP(Fe)@luminol@GOD was introduced to the detection system containing glucose, substantial H2O2 was released under the catalysis of GOD on Co-TCPP(Fe). Then, the produced H2O2 was decomposed by the 2D-MOF nanosheet, and the luminol on Co-TCPP(Fe)@luminol@GOD was further oxidized, generating a chemiluminescence signal, finally achieving rapid determination of glucose. Under the optimized condition, fabrication of 2D-MOF nanosheets as sensitive glucose sensors exhibited good performance during the process: (i) good sensitivity (LOD, 10.667 μg/L) with a wide linear range (32–5500 μg/L); (ii) satisfactory accuracy (recoveries, 89–121.2%; CV, 3.5–7.4%); (iii) low cost; and (iv) simple operation. Our proposed method here has the potential for screening glucose in various human urine samples from hospitals.