A highly sensitive upconversion nanoparticles@zeolitic imidazolate frameworks fluorescent nanoprobe for gallic acid analysis

Portable multimodal platform with carbon nano-onions as colorimetric and fluorescent signal output for trypsin detection

Multimodal biosensors with independent signaling pathways can self-calibrate and improve the reliability of disease biomarker detection. Herein, a colorimetric-fluorescent dual-mode paper-based biosensor with PAN/Fe(III)-CNOs (FPCs) as core components has been developed, which information is recognized by smartphone and naked eye. Using 1-(2-pyridylazo)-2-naphthol (PAN) as a mediator, Fe(III) is enriched on the surface of carbon nano-onions (CNOs), endowing FPCs with excellent mimetic enzyme activity and photothermal conversion ability, which allows it to output amplified colorimetric signals under laser irradiation. In addition, the complexation of PAN with Fe(III) broadens its absorption spectrum, which makes FPCs more suitable to be energy acceptors to quench fluorescence of polymer dots (Pdots), resulting in the changes of output fluorescent signal. Based on the above design, a portable colorimetric-fluorescent dual-mode biosensor is proposed for trypsin detection with Pdots as fluorescence sources and FPCs as fluorescence quenchers and nanoenzymes. This work provides a convenient way for constructing portable visual multimodal biosensors, which is expected to applied in various disease diagnosis.

Cobalt oxyhydroxide nanoflakes enable ratiometric fluorescent assay of gallic acid

Gallic acid (GA) is widely used in beverages, food, and other fields as antioxidant. However, GA is slightly toxic and the accumulation of GA is harmful to human body. Therefore, it's vital to develop simple and sensitive detection methods for GA. In this work, a novel ratiometric fluorescent nanoprobe (named CoOOH/OPD/SiNPs) for the GA detection in different foods was designed and prepared. The fluorescence of silicon nanoparticles (SiNPs) at 443 nm would be quenched by cobalt oxyhydroxide (CoOOH) nanoflakes. o-phenylenediamine (OPD) would be oxidized to 2,3-diaminophenazine (DAP) by CoOOH nanoflakes that have peroxidase-like activity, which produces a new fluorescent peak at 556 nm. Meanwhile, SiNPs' fluorescence would be quenched through DAP due to inner filter effect (IFE). With the addition of GA, the reductive decomposition of CoOOH decreased DAP level, causing IFE being restrained. The concentration of GA indicates an excellent linear relationship with fluorescence ratio (F443/F556) in range of 0.4-12 μM (R2 = 0.9937) with 0.16 μM detection limit. This nanoprobe is applied to GA detection in water, tea leaves, fruits and nut fruits, which would be expected to act as a portable device for complex substances analysis.

The Art of Nanoparticle Design: Unconventional Morphologies for Advancing Luminescent Technologies

The advanced design of rare-earth-doped (RE-doped) fluoride nanoparticles has expanded their applications ranging from anticounterfeiting luminescence and contactless temperature measurement to photodynamic therapy. Several recent studies have focused on developing rare morphologies of RE-doped nanoparticles. Distinct physical morphologies of RE-doped fluoride materials set them apart from contemporary nanoparticles. Every unusual structure holds the potential to dramatically improve the physical performance of nanoparticles, resulting in a remarkable revolution and a wide range of applications. This comprehensive review serves as a guide offering insights into various uniquely structured nanoparticles, including hollow, dumbbell-shaped, and peasecod-like forms. It aims to cater to both novices and experts interested in exploring the morphological transformations of nanoparticles. Discovering new energy transfer pathways and enhancing the optical application performance have been long-term challenges for which new solutions can be found in old papers. In the future, nanoparticle morphology design is expected to involve more refined microphysical methods and chemically-induced syntheses. Targeted modification of nanoparticle morphology and the aggregation of nanoparticles of various shapes can provide the advantages of different structures and enhance the universality of nanoparticles.

Natural Polymer Encapsulated Zeolitic Imidazolate Framework-12 Composite toward Electrochemical Sensing of Antitumor Agent

Encapsulation of natural polymer pectin (Pec) into a zeolitic imidazolate framework-12 (ZIF-12) matrix via a simple chemical method toward anticancer agent gallic acid (GA) detection is reported in this work. GA, a natural phenol found in many food sources, has gained attention by its biological effects on the human body, such as an antioxidant and anti-inflammatory. Therefore, it is crucial to accurately and rapidly determine the GA level in humans. The encapsulation of Pec inside the ZIF-12 has been successfully confirmed from the physiochemical studies such as XRD, Raman, FTIR, and XPS spectroscopy along with morphological FESEM, BET, and HRTEM characterization. Under optimized conditions, the Pec@ZIF-12 composite exhibits wide linear range of 20 nM-250 μM with a detection limit of 2.2 nM; also, it showed excellent selectivity, stability, and reproducibility. Furthermore, the real sample analysis of food samples including tea, coffee, grape, and pomegranate samples shows exceptional recovery percentage in an unspiked manner. So far, there is little literature for encapsulating proteins, enzymes, metals, etc., that have been reported; here, we successfully encapsulated a natural polymer Pec inside the ZIF-12 cage. This encapsulation significantly enhanced the composite electrochemical performance, which could be seen from the overall results. All of these strongly suggest that the proposed Pec@ZIF-12 composite could be used for miniaturized device fabrication for the evaluation of GA in both home and industrial applications.

Ratiometric luminescent sensor based on BSA-coated gold/silver nanoclusters for the selective determination and spatiotemporal imaging of gallic acid in plants

A new fluorescence sensing strategy has been developed. Four bimetallic nanoclusters, gold/silver, gold/copper, gold/molybdenum and gold/cobalt, were prepared using bovine serum albumin (BSA) as a reducing and stabilizing agent. The fluorescence properties of four nanoclusters were explored by solid-state UV and XPS. The gold/silver nanoclusters (BSA-Au/Ag NCs) with the best ratiometric fluorescence properties for gallic acid (GA) in plants were selected to realize the sensitive detection of GA. GA affected the conformation of BSA, thereby disrupting the luminescent environment of the nanoclusters, resulting in a pronounced fluorescence quenching at 566 nm. The ratiometric fluorescence signal (I566/I453) was used for trace detection of GA in plants. It has a wide response range of 1.25-40.0 μM and a low detection limit of 45.27 nM. GA was detected at 19.49 μM in the plant extract, and the spiked recoveries ranged from 96.09 to 104.6%. In addition, due to the non-toxic and biocompatible properties of BSA, BSA-Au/Ag NCs have also been validated for fluorescence imaging of plant tissues. It realized the comparison of GA content in different parts of plants and the difference of GA content in plants after abiotic stress. Therefore, the developed strategy offers potential application for the analytical study of active substances in plants.

In situ growth of lanthanides-doped nanoparticles inside zeolites with enhanced upconversion emission for gallic acid detection

The combination of upconversion nanoparticles (UCNPs) with porous zeolites could enable the development of multifunctional composites and extend their optical applications in sensing, detection and biomedical monitoring. Herein, a series of high luminescent UCNPs@Zeolites nano-micro composites were constructed via the in situ growth strategy, by taking the low phonon-energy fluoride nanoparticles of NaLnF4 (Ln = Y, Gd) as doping hosts for Er3+/Yb3+, desilicated FAUY and ZSM-5 as the target zeolites. Benefiting from the formation of tightly combined interfaces between the UCNPs and the target zeolites that effectively passive the surface defects of UCNPs, three orders of magnitude of improved upconversion emission in maximum was obtained under 980 nm excitation through afterward heat treatment at 400 ℃. Moreover, the pre-exchange of Yb3+ into target zeolites before the in situ growth of UCNPs is another feasible approach to drastically improve the upconversion emission intensity of the UCNPs@Zeolites nano-micro composites. By taking NaGdF4:Yb,Er@DSZSM-5/HT as an example probe, the detection of GA was demonstrated and the detection ability of which is super than that of the corresponding bare NaGdF4:Yb,Er UCNPs. This research provided a universal approach to construct the UCNPs@Zeolites nano-micro composites with varied upconversion emission colors simply by choosing activator ions, which therefore indicates wide potential applications.

Fe/Mn Bimetal-Doped ZIF-8-Coated Luminescent Nanoparticles with Up/Downconversion Dual-Mode Emission for Tumor Self-Enhanced NIR-II Imaging and Catalytic Therapy

ZIF-8, as an important photoresponsive metal-organic framework (MOF), holds great promise in the field of cancer theranostics owing to its versatile physiochemical properties. However, its photocatalytic anticancer application is still restricted because of the wide bandgap and specific response to ultraviolet light. Herein, we developed lanthanide-doped nanoparticles (LDNPs) coated with Fe/Mn bimetal-doped ZIF-8 (LDNPs@Fe/Mn-ZIF-8) for second near-infrared (NIR-II) imaging-guided synergistic photodynamic/chemodynamic therapy (PDT/CDT). The LDNPs were synthesized by encapsulating an optimal Yb³⁺/Ce³⁺-doped active shell on the NaErF₄:Tm core to achieve dual-mode red upconversion (UC) and NIR-II downconversion (DC) emission upon NIR laser irradiation. At the optimal doping concentration, the UC and DC NIR-II emission intensities of LDNPs were increased 30.2- and 13.2-fold above those of core nanoparticles, which endowed LDNPs@Fe/Mn-ZIF-8 with an outstanding capability to carry out UC-mediated PDT and NIR-II optical imaging. In addition, the dual doping of Fe²⁺/Mn²⁺ markedly decreased the bandgap of the ZIF-8 photosensitizer from 5.1 to 1.7 eV, expanding the excitation threshold of ZIF-8 to the visible light region (∼650 nm), which enabled Fe/Mn-ZIF-8 to be efficiently excited by UC photons to achieve photocatalytic-driven PDT. Furthermore, Fe²⁺/Mn²⁺ ions could be responsively released in the tumor microenvironment through degradation of Fe/Mn-ZIF-8, thereby producing hydroxyl radicals (·OH) by Fenton/Fenton-like reactions to realize CDT. Meanwhile, the degradation of Fe/Mn-ZIF-8 endowed the nanosystems with tumor self-enhanced NIR-II imaging function, providing precise guidance for CDT/PDT.

Investigation on the Peroxidase-like Activity of Vitamin B6 and Its Applications in Colorimetric Detection of Hydrogen Peroxide and Total Antioxidant Capacity Evaluation

The peroxidase-like activity of vitamin B6 (VB6) was firstly demonstrated by catalyzing the peroxidase chromogenic substrate 3,3′,5,5′-tetramethylbenzidine (TMB) at the existence of H2O2. The influence of different factors on the catalytic property of VB6, including pH, temperature, VB6 concentration, and incubation time, were investigated. The steady-state kinetic study results indicate that VB6 possesses higher affinity to H2O2 than natural horseradish peroxidase and some other peroxidase mimics. Besides, the radical quenching experiment results confirm that hydroxyl radical (•OH) accounts for the catalytic process. Based on the excellent peroxidase-like catalytic activity of VB6, the colorimetric methods for H2O2 and gallic acid (GA) detection were developed by measuring the absorbance variance of the catalytic system. Under the optimal conditions, the linear ranges of the methods for H2O2 and GA determination with good selectivity are 50.0–600.0 μM and 10.0–50.0 μM, respectively. In addition, the developed method was applied in the detection of H2O2 in milk samples and evaluation of total antioxidant capacity of different tea infusions. This study may broaden the application prospect of VB6 in environmental and biomedical analysis fields, contribute to profound insight of the physiological functions of VB6, as well as lay foundation for further excavation of small-molecule peroxidase mimics.

AuPd nanoparticles functionalized core-shell Co3O4/ZnO@ZnO for ultra-sensitive toluene detection

In this work, core-shell AuPd nanoparticles (NPs) sensitized Co₃O₄/ZnO@ZnO ellipsoid nanoparticles was successfully synthesized via a simple liquid phase synthesis method. SEM and TEM characterization results showed that the as-prepared samples have core-shell ellipsoid morphology and the size of the nanoparticles were uniform. Systematic gas sensing characterization was carried out to obtain the gas sensing property of AuPd NPs decorated Co₃O₄/ZnO@ZnO. It was found that the gas sensing property could be significantly enhanced after noble metal decoration with Au, Pd and AuPd NPs, respectively. The optimal gas sensing performance was achieved by AuPd NPs functionalized Co₃O₄/ZnO@ZnO based gas sensor. The maximum response reached 256-100 ppm toluene at 250 °C, which is 50 °C lower than pure ZnO. The detection limit of AuPd functionalized Co₃O₄/ZnO@ZnO was as low as 100 ppb. The enhanced sensing mechanism was mainly attributed to the synergistic effect of Au and Pd, which was detailly discussed in gas sensing mechanism part.

Functional Hybrid Micro/Nanoentities Promote Agro-Food Safety Inspection

The rapid development of nanomaterials has provided a good theoretical basis and technical support to solve the problems of food safety inspection. The combination of functionalized composite nanomaterials and well-known detection methods is gradually applied to detect hazardous substances, such as chemical residues and toxins, in agricultural food products. This review concentrates on the latest agro-food safety inspection techniques and methodologies constructed with the assistance of new hybrid micro/nanoentities, such as molecular imprinting polymers integrated with quantum dots (MIPs@QDs), molecular imprinting polymers integrated with upconversion luminescent nanoparticles (MIPs@UCNPs), upconversion luminescent nanoparticles combined with metal-organic frameworks (UCNPs@MOFs), magnetic metal-organic frameworks (MOFs@Fe₃O₄), magnetic covalent-organic frameworks (Fe₃O₄@COFs), covalent-organic frameworks doped with quantum dots (COFs@QDs), nanobody-involved immunoassay for fast inspection, etc. The presented summary and discussion favor a relevant outlook for further integrating various disciplines, like material science, nanotechnology, and analytical methodology, for addressing new challenges that emerge in agro-food research fields.