Portable hydrogel test kit integrated dual-emission coordination polymer nanocomposite for on-site detection of organophosphate pesticides.

It is of great significance to on-site detection of organophosphate pesticides (OPs) for pollution monitoring and poisoning estimation. Herein, we developed a portable hydrogel test kit for on-site detection of OPs, which is based on the integration of agarose hydrogel with dual-emission coordination polymers (CPs) nanocomposite comprised of Ru(bpy)32+ and zinc (II)-based CPs (ZnCPs) loaded with thioflavin T (ThT). Different from Ru(bpy)32+ with stable fluorescence in acidic environment, ThT@ZnCPs is highly sensitive to H+, which destroys the structure of ZnCPs as a host and quenches ThT@ZnCPs fluorescence. The distinct fluorescence behaviors of Ru(bpy)32+ and ThT@ZnCPs in acidic environment enable the hydrogel test kit to exhibit ratiometric fluorescence responses to acetylcholinesterase (AChE), which hydrolyzes acetylcholine to acetic acid and provides H+. On this basis, combining the inhibition effect of OPs to AChE activity, a ratiometric fluorescence method for OPs detection was established with the hydrogel test kit, and satisfactory results have been achieved in buffered aqueous solutions and apple juice samples. Attractively, by employing smartphone as a signal readout, on-site quantitation of OPs was accomplished with the features of easy to use, portability and low cost, demonstrating a great promising for point-of-care testing in food safety monitoring.

Integrated enzyme with stimuli-responsive coordination polymer for personal glucose meter-based portable immunoassay.

Coordination polymers (CPs) with tunable structures and properties have been extensively explored in a variety of fields. In this work, we demonstrated the potential of stimuli-responsive CPs as a host of integrating enzymes to construct a portable immunoassay. By employing terbium ion (Tb3+) as a metal node and guanine monophosphate (GMP) as a bridge ligand, an alkaline phosphatase (ALP)-responsive Tb/GMP CPs was fabricated, which allows amyloglucosidase (GA) to be integrated to form GA@Tb/GMP composite. Owing to the size-selectivity of Tb/GMP CPs as a host, the loaded GA was physically isolated from its substrate starch. However, Tb/GMP CPs is highly sensitive to ALP, which can hydrolyze the phosphate group of GMP to destroy the structure of Tb/GMP CPs, leading to the release of GA from GA@Tb/GMP composite. The released GA can digest starch to produce glucoses and give a measured signal by personal glucose meter (PGM). This finding leads to a PGM-based portable immunoassay for the quantitative analysis of carcinoembryonic antigen (CEA), and satisfactory results with a detection limit of 0.28 ng/mL have been achieved. The successful determination of CEA in serum samples demonstrates its potential in practical application. We believe that this work can provide a remarkable insight for the rational design of stimuli-responsive CPs for a wide of applications.

Visual detection of alkaline phosphatase based on ascorbic acid-triggered gel-sol transition of alginate hydrogel.

Stimuli-responsive hydrogel has been emerged as a popular tool for chemical sensing due to its unique mechanical properties. In this work, we fabricated an ascorbic acid (AA)-responsive alginate hydrogel for the visual detection of alkaline phosphatase (ALP). This alginate hydrogel (RhB@Alg/Fe3+) was crosslinked with Fe3+, and rhodamine B (RhB) was encapsulated into the hydrogel as an indicating reagent to assistant visual detection. Because of the weak affinity of Fe2+ to alginate, the presence of reductive AA can trigger the dissolution of RhB@Alg/Fe3+ to give an observable red color in the sol solution. On this basis, by using ascorbic acid 2-phosphate as a substrate of ALP, which can be hydrolyzed by ALP to produce AA, the gel-sol transition process of RhB@Alg/Fe3+ was further modulated by ALP. This finding leads to a simple visual method for ALP detection with a low detection limit of 0.37 mU/mL and an excellent selectivity over other proteins. Compared with conventional colorimetric assays, this visual sensor shows the distinct advantages of simple fabrication, cost-effectiveness and easy to implement. We believe that this study can provide a new insight into the fabrication of responsive alginate hydrogel for promising applications in chemical sensing and biomedical fields.

Time-Resolved Fluorescence Detection of Superoxide Anions Based on an Enzyme-Integrated Lanthanide Coordination Polymer Composite.

In this work, we proposed a new strategy of fabricating time-resolved fluorescent nanoprobes by using an enzyme-integrated lanthanide coordination polymer (CP) composite for the detection of superoxide anions (O2•-). This CP composite was constructed with terbium ions (Tb3+) as a metal node, adenosine triphosphate (ATP) as a bridge ligand, and carboxyphenylboronic acid (CPBA) as a sensitizer in which superoxide dismutase (SOD) was encapsulated by a self-adaptive inclusion process. The as-prepared SOD@ATP/Tb-CPBA displays both catalytic and fluorescence properties. Benefiting from the shielding effect of ATP/Tb CP, greatly enhanced catalytic activity and stability against harsh environments can be obtained in the loaded SOD. Meanwhile, the loaded SOD can remove the water molecules on the coordination sphere of Tb3+, leading to a significant increase in the fluorescence intensity and lifetime of SOD@ATP/Tb-CPBA. However, upon the addition of O2•-, the fluorescence of SOD@ATP/Tb-CPBA was quenched significantly. This is because SOD can convert O2•- into H2O2 to induce the deboronation of CPBA, resulting in an intramolecular charge transfer process. On this basis, by taking advantage of Tb3+ in long lifetime emission, a time-resolved fluorescence method was developed for the detection of O2•-, and satisfactory results have been achieved in both buffered aqueous solutions and serum samples. We believe that the presented study will open up a new avenue to develop enzyme-involved fluorescent nanoprobes.

Self-Assembled FRET Nanoprobe with Metal-Organic Framework As a Scaffold for Ratiometric Detection of Hypochlorous Acid.

Metal-organic framework (MOF) has been extensively explored in a number of fields due to its diverse properties. In this work, we demonstrated the potential of MOF in the establishment of a self-assembled fluorescence resonance energy transfer (FRET) system for developing ratiometric fluorescent nanoprobe. For this purpose, zeolitic imidazolate framework-8 (ZIF-8) was selected as a MOF model to entrap carbon dot (CD) and curcumin (CCM) during its self-assembly, which produces CD/CCM@ZIF-8. Benefiting from the confinement effect of ZIF-8, the loaded CD and CCM can be brought in close proximity for energy transfer to occur. Under optimal conditions, a high FRET efficiency of 68.7% can be obtained. Importantly, compared with traditional FRET systems, the fabrication process of CD/CCM@ZIF-8 is much more simple and straightforward, which does not involve the elaborate design and complicated synthesis of molecular linkers. However, in the presence of hypochlorous acid (HClO), the FRET process from CD to CCM will be disrupted, rendering CD/CCM@ZIF-8 to display a ratiometric response to HClO. This finding led to a method for ratiometric fluorescent detection of HClO with a detection limit of 67 nM and excellent selectivity over other reactive oxygen species. We believe that this study can give a new insight into the rational design and application of FRET-based nanoprobes.

Pyrophosphate ion-responsive alginate hydrogel as an effective fluorescent sensing platform for alkaline phosphatase detection.

A pyrophosphate ion (PPi)-responsive alginate hydrogel was fabricated by using Cu2+ as a crosslinker. Benefiting from the ultrahigh affinity of Cu2+ to PPi, which can discriminate PPi from phosphate ions and other anions, the incorporation of carbon dots enables the alginate hydrogel to be an effective fluorescent sensing platform for the detection of alkaline phosphatase.