Colorimetric Probe Research Articles

Recent Development of Electrospun Nanostructured Fibers as Colorimetric Probes for Metal Ion Sensing: A Review

Recent Development of Electrospun Nanostructured Fibers as Colorimetric Probes for Metal Ion Sensing: A Review

Colorimetric aptasensor based on Fe3O4@MOF@Pt nanozymes for ultrasensitive detection of histamine in fish

The accurate determination of histamine in fish is imperative for food safety, given the toxic nature of this biogenic amine. This study presents an innovative colorimetric aptasensor for the ultrasensitive detection of histamine in fish, utilizing nanozymes based on magnetic metal-organic frameworks coated with Pt nanoparticles (Fe3O4@MOF@Pt), which exhibit high peroxidase-like catalytic activity, magnetism, and superior optical properties. The surface of Fe3O4@MOF@Pt nanozymes were modified with DNA strands complementary to the histamine aptamer, creating effective colorimetric probes. In the presence of histamine, these colorimetric probes compete with histamine molecules for aptamer binding on the enzyme plate. Color development is triggered by adding a TMB and H2O2 substrate solution to the enzyme plate. This competitive binding-based aptasensor allows for rapid and accurate histamine quantification within a linear range of 10 pM to 10 μM, and a notable detection limit of 6.23 pM. Furthermore, the sensor demonstrated excellent specificity, distinguishing histamine from l-histidine and other biogenic amines. Tested on mackerel samples, the aptasensor showed spiked recoveries of 91.4%–109.6%, validating its practical applicability. This sensor offers an ultrasensitive, specific, and reusable tool for histamine detection, representing a significant advancement in ensuring the safety of fish products.

Facile colorimetric sensor development for sequential detection of coralyne and calf-thymus DNA via tannic acid-assisted silver nanoparticles

Owning to unique size dependent optical properties, plasmonic nanoparticles have been explored as chemical read-outs for assaying various biological and chemical analytes. We propose colorimetric sensing strategy based on tannic acid mediated silver nanoparticles (TA-AgNPs) for the detection of Coralyne (COR) and calf thymus DNA (CT-DNA). Aggregation of TA-AgNPs is observed on addition of COR molecule because of electrostatic interaction between them, which is established by change in color from yellow to brown. TA-AgNPs/COR based colorimetric probe was then employed for CT-DNA detection, utilizing anti-aggregation of nanoparticles. Formation of intercalated complex between CT-DNA and COR prevents the aggregation of nanoparticles and color of TA-AgNPs solution remains yellow. Under optimum sensing conditions, extent of aggregation and anti-aggregation of TA-AgNPs was studied. A linear correlation between absorbance value at 437 nm and COR concentration is obtained in the range of 0 to 1.2 μM with detection limit of 0.44 μM. TA-AgNPs/COR based detection probe exhibited linear response to CT-DNA in concentration range of 0 to 7.62 μM with a limit of detection down to 1.63 μM. The applicability of sensing strategy verified by analysis of COR and CT-DNA in human urine samples, which demonstrated the practical utility of method in biomedical applications.

A highly sensitive and colorimetric fluorescent probe for visualizing hydroxylamine in immune cells

BackgroundHydroxylamine (HA) is vital industrial raw material and pharmaceutical intermediate. In addition, HA is an important cellular metabolite, which is intermediate in the formation of nitric oxide and nitroxide. However, excessive amounts of HA are toxic to both animals and plants. Conventional methods for the detection of HA are cumbersome and complicated. The detection of HA with fluorescent probes is convenient and sensitive. There are few probes available for the detection of hydroxylamine. Therefore, a fluorescent probe for the sensitive and selective detection of HA was developed in this work. ResultsA coumarin derivative SWJT-22 was synthesized as a colorimetric fluorescent probe to detect hydroxylamine (HA), with high sensitivity and selectivity. The detection limit of the probe to HA was 0.15 μM, which was lower than most probes of HA. Upon the addition of HA to aqueous solution containing SWJT-22, the color of the solution changed from orange to yellow, and the fluorescence color also changed from orange to green. The reaction mechanism of SWJT-22 to HA was confirmed by 1H NMR titrations, mass spectrometry and round bottom flask experiments. Moreover, SWJT-22 had been fabricated into portable test strips for the detection of HA. SWJT-22 had been successfully used in cellular imaging and could detect both endogenous and exogenous HA in HeLa cells and RAW 264.7 cells. SignificanceDue to the physiological role of hydroxylamine in organisms, it is crucial to detect hydroxylamine selectively and sensitively. This work provided a convenient tool for the detection of hydroxylamine, not only to detect endogenous and exogenous HA in cells, but also made into portable test strips. The HA fluorescent probe SWJT-22 is expected to promote the study of HA in physiological processes.

A dual responsive bis-thiophene affixed thiosemicarbazide based chemosensor for colorimetrically Hg2+ and fluorometrically Cu2+ ions and their applications in live cell imaging

In this work, we developed a fast and straightforward colorimetric and photoluminescent chemosensor probe (P1), featuring bis-thiophene-thiosemicarbazide moieties as its signaling and binding unit. This probe exhibited rapid sensitivity to Hg2+ and Cu2+ ions in a semi-aqueous medium, resulting in distinct colorimetric and photoluminescent changes. In the presence of Cu2+, P1 displayed an impressive 50-fold increase in photoluminescence (PL) at 450 nm (with excitation at 365 nm). The probe P1 formed a 1:1 complex with Hg2+ and Cu2+ ions, featuring association constant values of 4.04 × 104 M−1 and 1.25 × 103 M−1, respectively. P1 has demonstrated its efficacy in the analysis of real samples, yielding promising results. Additionally, the probe successfully visualized copper ions on a mouse fibroblast cell line (NIH3T3), highlighting its potential as an intracellular probe for copper ion detection.

A novel “ON-OFF-ON” colorimetric and fluorescence dual-signal sensing APAP based on TSPP-Fe3+

Acetaminophen, also known as paracetamol (APAP), is a commonly used over-the-counter medication that is often used to treat headaches, toothaches, joint pain, muscle pain, and to lower body temperature. However, overdose can lead to liver damage, gastrointestinal distress, kidney damage, and cardiovascular disease. Therefore, it is very important to establish a method to quickly detect APAP. A novel “ON-OFF-ON” colorimetric and fluorescence dual-signal sensing system was constructed for the quantitative detection of APAP based on 5,10,15,20-tetrakis(4-sulphonatophenyl) porphyrin (TSPP) dual-signal probe. The absorbance and fluorescence intensity of TSPP respectively were quenched when Fe3+ was introduced into TSPP solution. At this point, the color of the corresponding solution changed from red to green. The absorbance and fluorescence intensity of TSPP respectively were restored when APAP was added to the TSPP-Fe3+ system. At this time, the color of the solution changed from green to colorless. Therefore, an “ON-OFF-ON” dual-signal sensing study of APAP were constructed using TSPP as the colorimetric and fluorescent probe. The proposed colorimetric sensing system had a wide linear range in the 13.12 mM ∼ 23.20 mM with 0.11 mM of limit of detection (LOD, S/N = 3). And the proposed fluorescence sensing system had a wide linear range in the 3.45 mM ∼ 12.50 mM and 41.67 mM ∼ 65.22 mM with 0.83 mM of limit of detection (LOD, S/N = 3). The dual-signal sensing system were applied to the APAP detection of real samples.

A dual-signals fluorometric and colorimetric peptide-based probe for Cu(II) and glyphosate detection and its application for bioimaging and water testing

A novel dual-signal fluorometric and colorimetric probe FMDH (5-FAM-Met-Asp-His-NH2), incorporating a tripeptide (Met-Asp-His-NH2) linked to 5-carboxyfluorescein (5-FAM), was firstly synthesised. FMDH demonstrated exceptional selectivity and sensitivity, rapid response, wide pH response range and robust anti-interference capabilities for monitoring Cu2+. This was achieved through a distinctive naked-eye colorimetric and fluorescent quenching behaviour. A good linearity within the range of 0–3 μM (R2 = 0.9914) was attained, and the limit of detection (LOD) for Cu2+ was 47.4 nM. Furthermore, the FMDH-Cu2+ ensemble responded to glyphosate with notable selectivity and sensitivity. A good linear correlation (R2 = 0.9926) was observed at the lower concentration range (2.4–7.8 μM) and achieving a detection limit as low as 29.9 nM. The response time of FMDH with Cu2+ and glyphosate were less than 20 s, and the pH range of 7–11 that was suitable for practical application under physiological pH conditions. MTT assays confirmed that FMDH offers good permeability and low toxicity, facilitating successful application in imaging analysis of Cu2+ and glyphosate in living cells and zebrafish. In addition, FMDH was employed in the detection of these analytes in real water samples. Cost-effective, highly sensitive and easily prepared FMDH-impregnated test strips were developed for the efficient visual detection of Cu2+ and glyphosate under 365 nm UV light. Increasing concentrations of Cu2+ and glyphosate resulted in notable colour changes under 365 nm UV light, enabling visual semi-quantitative analysis via a smartphone colour-analysis App.

A colorimetric/down-conversion fluorescence dual-readout probe for the recognition of Cu2+ and its application in environmental water by single PEI@NaYF4: Eu3+ nanoparticles

The pollution caused by heavy metals like Cu2+ remains a pressing issue, as the release of Cu2+-laden sewage can lead to detrimental effects on both soil ecosystems and human well-being. Herein, a novel colorimetric and down-conversion fluorescence probe, i.e. PEI@NaYF4: Eu3+ NPs, for selective and sensitive detection of Cu2+ with colorimetric and down-conversion fluorescence dual signal changes was reported. Such dual-signal detection mode offers enhanced sensitivity, accuracy, and cost-effectiveness in detecting Cu2+. The probe with spherical shape and excellent monodispersity was synthesized by a high temperature reflux method. The PEI moiety of the NPs is chosen due to the ability to chelate Cu2+ forming copper amine complexes. Such a unique feature is invoked to develop a versatile detection platform for the colorimetric detection of Cu2+ ions. In the presence of Cu2+, the visual color of probe in solution changes from colorless to blue with a low detection limit of 100 nM without any assistance of equipment. The probe emits down-conversion fluorescence with two main typical emission peaks centered at 592 and 614 nm under an excitation of 394 nm. The copper amine complexes formed by the combination of Cu2+ and the PEI moiety of the NPs quench down-conversion fluorescence by an internal filtration effect. Probe shows a specific on–off response to Cu2+ in aqueous solution with nanomolar LOD, fast response, and good selectivity, and without interference by a range of metal ions. A practical application shows that PEI@NaYF4: Eu3+ NPs have good recovery ranges of 96–105 % for Cu2+ detection in real environment water samples from different locations. This strategy proves that a colorimetric and down-conversion fluorescence probe is a potential tool for addressing heavy metal ions-induced water pollution.

Colorimetric Sensor for Cr(VI) Ion Detection in Tap Water Using a Combination of AuNPs and AgNPs.

Colorimetric sensors are a promising technique for the simple screening of water, food, and environmental samples contaminated with interferents, allowing for color changes to be observed with the naked eye or a spectrophotometer. In this study, a colorimetric sensor for the selective detection of hexavalent chromium ion (Cr(VI)) contamination in water was developed. A combination of sodium borohydride-coated gold and citrate-capped silver nanoparticles (Na-AuNPs/cit-AgNPs) was employed as a colorimetric probe. Upon the addition of Cr(VI)-contaminated tap water in the colorimetric probe solution, the color sequentially transitioned from its initial orange to dark reddish-purple, dark purplish-red, dark blue-violet, and gray. This colorimetric strategy relies on AgNP dissolution and AuNP aggregation in the presence of the Cr(VI) ions. The dissolution of AgNPs is evidenced by the reduction of the characteristic peak of AgNPs at 400 nm, while the aggregation of AuNPs leads to a red shift in the absorption band at 514 nm, accompanied by broad absorption in the 500-700 nm range. The limits of detections were found to be 22.9 and 50 ppb using a spectrometer and by visual observation, respectively. The synthesized AuNPs and AgNPs are very stable in the presence of media containing complicated ions. We further demonstrated the practical applicability of the developed system for detecting Cr(VI) in real samples, including natural water and artificial urine, highlighting its potential for addressing Cr(VI) contamination in practical scenarios.

Highly selective colorimetric and fluorescent probe for F− and P2O74− based on AIEE and dual ESIPT

In this study, the Schiff base (probe 1) was designed and synthesized, using the moieties of benzothiazole and salicylaldehyde as signaling units. UV–visible and emission spectroscopy has been identified to study interaction of probe 1 with various anions. Absorption bands at 290 and 360 nm for probe 1 (20 µM; CH3CN) were observed and two fluorescence peaks at 415 and 540 nm obtained with excitation at 360 nm in CH3CN. Probe 1 (20 µM) developed a yellow color in presence of F− and P2O74− ions in their tetrabutylammonium salts. For both the ions, the corresponding absorption measurements revealed bathochromic shift of 85 nm. When complexed with anions, emission changes show that probe 1 acts as a “turn-on” sensor. Probe 1 shows detection limit (LOD) of 35.4 and 15.4 nM for F− and P2O74−, respectively. 1H NMR titration analyses revealed more about their mode of binding with probe 1.

A colorimetric and ratiometric fluorescent probe for recognizing fluoride ion based on new chromophore reaction

Fluoride ion plays crucial roles in many biological, chemical, medical and environmental processes. Constructing a highly sensitive florescent probe for naked-eye detection F− is of particular importance but remains challenging. In this work, we developed a colorimetric and ratiometric fluorescent probe of pyrrolopyrrole aza-BODIPY (PPAB)-based polymer (P1) for recognizing F−. In presence of F−, P1 showed obvious color change from green to yellow with absorption maximum blueshift from 670 nm to 340 nm. The weak emission of 697 nm changed to strong orange fluorescence with appearance of new broad emission with maximum bands at 520 and 642 nm. P1 was capable of sensitively and selectively detecting F− with a low detection limit of 0.07 μM. The sensing mechanism revealed that B–N bond cleavage and following hydrolysis of P1 induced by F− was responsible for the distinct colorimetric and ratiometric fluorescent signals. The results indicated that PPAB core was an efficient recognition unit for F− detection for the first time. Finally, P1-loaded silicone or test paper could detect F− by naked-eye signals. The probe can be successfully applied in real water samples to detect F− concentration.

Near-infrared colorimetric fluorescent probe for detecting HSO3− and its practical application

A colorimetric near-infrared fluorescent probe was designed and synthesized in this paper. The probe XCCC was obtained by simple condensation of 6-(diethylamino)-2,3-dihydro-1H-xanthene-4-carbaldehyde and 3-cyanoacetyl indoles. XCCC detects HSO3− through 1, 4-nucleophilic addition reaction, with obvious near-infrared fluorescence quenching (λem = 696 nm), and the solution color changes from pink to pale yellow under natural light to realize naked eye recognition. In addition, XCCC has a super large Stokes shift value (196 nm) by calculation. The sensitivity of XCCC and HSO3− in the concentration range of 0 ∼ 60 μM is excellent, and the LOD value is as low as 11.4 nM. It is very fast for XCCC to detect HSO3− in real time (30 s), and the reversible cycle of HSO3−- H2O2 is realized (5 times). In practical application, XCCC successfully detected HSO3− qualitatively and quantitatively in actual water samples. Furthermore, we made XCCC into fluorescent test strips to qualitatively detect HSO3− in red wine. In particular, XCCC was used to realize exogenous cell imaging of HSO3− with different concentrations and reversible cell imaging of HSO3−-H2O2 in A549 cells. It shows that probe XCCC has a potential application prospect in food samples and life systems.

Chemical Synthesis of Bimetallic Ag/Co Nanoparticles for Colorimetric Detection of Cr3+ and Fe3+ and Its Catalytic Performance

Precious metal nanoparticles, especially Ag-based nanoparticles due to their strong surface plasma effect and excellent catalytic performance, have been widely applied in environmental remediation and detection of heavy metal ions in aqueous solution. In this study, first, bimetallic Ag/Co nanoparticles (Ag/Co NPs) modified by sodium citrate were synthesized by chemical reduction method. Second, bimetallic Ag/Co NPs were used as colorimetric probe for detecting [Formula: see text] and [Formula: see text] in aqueous solution simultaneously for the first time. The results showed that the probe had high specificity towards [Formula: see text] and [Formula: see text] among the tested metal ions. When [Formula: see text] was mixed with Ag/Co NPs, the solution quickly changed from yellow to pink, meanwhile, the UV–Vis absorption intensity declined at 400[Formula: see text]nm and a new prominent absorption band was formed at 530[Formula: see text]nm. While [Formula: see text] was mixed with Ag/Co NPs, the solution quickly changed from yellow to nearly colorless. The linear relationship between absorbance of bimetallic Ag/Co NPs at 400[Formula: see text]nm and −log of [Formula: see text] concentration is 1[Formula: see text]nM to 10[Formula: see text][Formula: see text]M, which [Formula: see text] and [Formula: see text]. The limit of detection (LOD) for this study was 1.14[Formula: see text]nM. Similar to [Formula: see text], the LOD for [Formula: see text] was calculated 16.3[Formula: see text][Formula: see text]M. In addition, the catalytic performance of bimetallic Ag/Co NPs was evaluated by methylene blue (MB) in the presence of H2O2. The catalytic degradation efficiency of bimetallic Ag/Co NPs was about 4.8 times greater than monometallic Ag NPs, confirming Ag and Co NPs had obviously synergistic effect. Therefore, this result made bimetallic Ag/Co NPs had potential application in the field of environmental remediation.

Highly dispersed Pt nanoparticles onto dendritic silica as colorimetric probe for CO sensing in mainstream cigarette smokes

Carbon monoxide (CO) is a typical substance harmful to human body produced during cigarette smoking. Its content in cigarette smoke is one of the important indicators for evaluating its toxicity and the filtration effect of cigarette filter tips, which provides important guidance for its rational design. In this work, Pt nanoparticles with superior peroxidase catalytic ability were synthesized and loaded onto fibrous SiO2 nanoparticles as nanozymes to detect CO in cigarette smoke by taking advantage of the reduced catalytic performance of CO adsorption on the active sites of the nanozymes. The fibrous SiO2 not only provide abundant sites for the deposition and dispersion of Pt NPs, but also prevent their aggregation and thus maintain their high catalytic activity. Density functional theory calculations reveal that Pt nanoparticles exhibits superior peroxidase ability over Au and Pd nanoparticles, which can be significantly inhibited by CO. Accordingly, a nanozyme-inhibition based colorimetric method was developed for the detection of CO in cigarette smoke with the limit of detection of 0.15 mg/L. The applicability of this method was validated by analyzing the CO contents in 8 kinds of cigarette smoke with different types of filter tips. The concentrations of CO are in the range of 5.40–6.73 mg/branch, which are in good agreement with those of GC results, indicating the accuracy and reliability of our method. This assay is fast, convenient and sensitive for quantitatively assessing the CO content in cigarette smoke, and it lays the foundation for prompting the widespread use of nanozyme-inhibition in chemical sensing.

Bimetallic CuFe Prussian Blue Analogue Nanocubes as a Colorimetric Probe for the Quantification of Glutathione

Label-free bimetallic CuFe Prussian blue analogue nanocubes (CuFe PBA NCs) were directly employed as colorimetric probes for the visual determination of glutathione (GSH). CuFe PBA NCs produce an absorption peak at 400 nm. In the presence of GSH, the CuFe PBA NCs were transformed into larger hollow nanospheres based on the acid-initiated Kirkendall effect, leading to the appearance of a new peak at 520 nm and a solution color change from yellow to red. Thus, the GSH-induced color changes allowed the establishment of a double-signal colorimetric assay for GSH using the ratio of absorbance at 520 and 400 nm (Δ(A520/A400)). Facile determination of GSH from 0.1 to 8 μM with satisfactory specificity was developed, providing a detection limit as low as 0.08 μM. Additionally, GSH concentrations exceeding 3 μM can be directly identified by the naked eye. The colorimetric assay for GSH has also been demonstrated to have application for serum analysis. Compared with conventional single-signal colorimetric determination, the ratiometric probe was demonstrated to provide good selectivity and high sensitivity.

Developing new Hydrazine Carbothioamide Molecules for Selective Colorimetric/Fluorometric Detection of Environmentally Essential Hg2+ and Ag+ Metal Ions in Mixed Aqueous Media.

A novel colorimetric and fluorogenic probe L based on hydrazine carbothioamide and 1,8-naphthalimide moieties has been designed and synthesized for the hypersensitive detection of Hg2+ or Ag+ ions. The observed probe L showed colorimetric and fluorometric responses for these studies when Hg2+ or Ag+ was added to the DMSO - HEPES buffer solution (pH = 7). An interference test with other metal ions was determined, and the high selectivity of Hg2+ and Ag+ did not interfere with other metal ions in colorimetric and fluorogenic methods. The possible mechanism of binding of these metal ions and the probe L 1:1 complex was determined by H1 NMR. Additionally, the reversibility of the affinity of probe L with mercury (Hg2+) and silver (Ag+) ions was investigated by adding Na2EDTA. The naked eye detected the "Off-On" type fluorescence sensor in the presence of Hg2+ and EDTA. The tested test strip kits provided a strong probability of probe L with high response and rapid, sensitive detection with Hg2+ ion, which may be suitable for practical use.

Nitrogen and Chlorine Co-Doped Carbon Dots with Yellow-Green Emission as a Ratiometric Fluorescent and Colorimetric Dual-Signal Probe for Quercetin Detection and Cell Imaging

Despite the emergence of numerous carbon dots (CDs)-based sensors, most of them are fluorescent probes. To improve the reliability of the results, using ratiometric fluorescence/UV-vis absorption dual-signal probes is an effective method. Herein, nitrogen and chlorine co-doped carbon dots (N, Cl-CDs) with yellow-green fluorescence were prepared and used as a dual-function probe for ratiometric fluorescence/UV-vis. The detection range of the fluorescence method was 0.05–78[Formula: see text][Formula: see text]M, and the limit of detection (LOD) was 1.2[Formula: see text]nM (3[Formula: see text]/s). For the colorimetric method, the linear range was 0.05–186[Formula: see text][Formula: see text]M with LOD of 10.7[Formula: see text]nM. Importantly, the N, Cl-CDs were successfully used to detect Quercetin (QT) in actual water samples. Besides, due to their good biocompatibility, the N, Cl-CDs were applied to in vivo biological imaging of oocysts and shown the potential for environmental survey and biological assay.

Prussian Blue Analogues-Derived Molecularly Imprinted Nanozyme Array for Septicemia Detection.

Septicemia, a severe bacterial infection, poses significant risks to human health. Early detection of septicemia by tracking specific biomarkers is crucial for a timely intervention. Herein, we developed a molecularly imprinted (MI) TiO2-Fe-CeO2 nanozyme array derived from Ce[Fe(CN)6] Prussian blue analogues (PBA), specifically targeting valine, leucine, and isoleucine, as potential indicators of septicemia. The synthesized nanozyme arrays were thoroughly characterized using various analytical techniques, including Fourier transform infrared spectroscopy, X-ray diffraction, field-emission scanning electron microscope, and energy-dispersive X-ray. The results confirmed their desirable physical and chemical properties, indicating their suitability for the oxidation of 3,3',5,5'-tetramethylbenzidine serving as a colorimetric probe in the presence of a persulfate oxidizing agent, further highlighting the potential of these arrays for sensitive and accurate detection applications. The MITiO2 shell selectively captures valine, leucine, and isoleucine, partially blocking the cavities for substrate access and thereby hindering the catalyzed TMB chromogenic reaction. The nanozyme array demonstrated excellent performance with linear detection ranges of 5 μM to 1 mM, 10-450 μM, and 10-450 μM for valine, leucine, and isoleucine, respectively. Notably, the corresponding limit of detection values were 0.69, 1.46, and 2.76 μM, respectively. The colorimetric assay exhibited outstanding selectivity, reproducibility, and performance in the detection of analytes in blood samples, including C-reactive protein at a concentration of 61 mg/L, procalcitonin at 870 ng/dL, and the presence of Pseudomonas aeruginosa bacteria. The utilization of Ce[Fe(CN)6]-derived MITiO2-Fe-CeO2 nanozyme arrays holds considerable potential in the field of septicemia detection. This approach offers a sensitive and specific method for early diagnosis and intervention, thereby contributing to improved patient outcomes.

Porphyrin-based covalent organic framework as oxidase mimic for highly sensitive colorimetric detection of pesticides.

A covalent organic framework-based strategy was designedfor label-free colorimetric detection of pesticides. Covalent organic framework-based nanoenzyme with excellent oxidase-like catalytic activity was synthesized. Unlike other artificial enzymes, porphyrin-based covalent organic framework (p-COF) as the oxidase mimic showed highly catalytic chromogenic activity and good affinity toward TMB without the presence of H2O2, which can be used as substitute for peroxidase mimics and H2O2 system in the colorimetric reaction. Based on the fact that the pesticide-aptamer complex can inhibit the oxidase activity of p-COF and reduced the absorbance at 650nm in UV-Vis spectrum, a label-free and facile colorimetric detection of pesticides was designed and fabricated. Under the optimized conditions, the COF-based colorimetric probe for pesticide detection displayed high sensitivity and selectivity. Taking fipronil for example the limit of detection was 2.7ng/mL and the linear range was 5-500,000ng/mL. The strategy was successfully applied to the detection of pesticides with good recovery , which was in accordance with that of HPLC-MS/MS. The COF-based colorimetric detection was free of complicated modification H2O2, which guaranteed the accuracy and reliability of measurements. The COF-based sensing strategy is a potential candidate for the sensitive detection of pesticides of interests.

Zirconium-porphyrin-MOF-based oxidase-like nanozyme with oxygen vacancy for aflatoxin B1 colorimetric sensing.

In this study, a porous coordination network zirconium-porphyrin-based nanoparticle with oxygen vacancies (OVs) was prepared using acetic acid and benzoic acid as modulators via a simple hydrothermal method. The presence of OVs was confirmed by various characterization methods and was found to enhance oxygen uptake and activation. This resulted in the generation of more reactive peroxyl radicals (•O2 -) and led to an improved oxidase (OXD) mimetic activity. Additionally, it promoted 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) oxidation, with a low Km value of 0.07mM and a high Vmax of 1.47×10-7M·s-1. As aflatoxin B1 (AFB1) inhibits the Pt@PCN-222-ABTS nanozyme system, a colorimetric probe for AFB1 detection was constructed. The limit of detection (LOD)was 0.074µg·L-1. This research presents a novel approach for designing a nanozymatic-based colorimetric method to analyze trace AFB1 residues in food.