Bioenzyme-free colorimetric assay for creatinine determination based on Mn3O4 nanoparticles catalyzed oxidation of 3,3',5,5'-tetramethylbenzidine.

Mn3O4 nanozyme with good oxidase-like activity was successfully synthesized. The prepared Mn3O4 nanozyme can directly and effectively catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to generate green-blue-colored ox-TMB. Creatinine exhibits distinct inhibition effect on Mn3O4 nanozyme-catalyzed TMB colorimetric reaction system, leading to obvious color fading and absorbance intensity decrease of the reaction system. Furthermore, interference from uric acid can be effectively eliminated by regulating the pH of TMB-Mn3O4 colorimetric reaction system to pH 2.0. Then, a simple and bioenzyme-free colorimetric assay for the determination of creatinine was developed based on TMB-Mn3O4 colorimetric reaction. The linear detection range is from 100 to 800 µM and from 1 to 20 mM. The lowest limit of detection is 35.3 µM. Satisfied results are obtained for the determination of creatinine in real urine and sweat samples. This work provides the synthesis of a good oxidase-like nanozyme Mn3O4 and presents the fabrication of an effective nanozyme-based bioenzyme-free colorimetric assay for the determination of creatinine.

TiO2 nanoparticles modified graphitic carbon nitride with potential-resolved multicolor electrochemiluminescence and application for sensitive sensing of rutin.

Recently, nanocomposites with potential-resolved multicolor electrochemiluminescence (ECL) property have attracted new research interests. Herein, TiO2 nanoparticles modified graphitic carbon nitride (TiO2-NPs/g-C3N4) with inherent potential-resolved multicolor ECL emission was prepared via a simple synthesis method. The morphology and chemical composition of the synthesized TiO2-NPs/g-C3N4 were characterized. The obtained TiO2-NPs/g-C3N4 exhibited dual-peak multicolor ECL emission under cyclic voltammetry scanning by using K2S2O8 as co-reagent. The first ECL peak (ECL-1) is composed of turquoise blue ECL emission (471 nm) located at -1.3 V and olive green ECL emission (490 nm) ranging from -1.4 to -2.0 V. The second ECL peak (ECL-2) is composed of navy blue ECL emission (458 nm) located at -3.0 V. The ECL mechanism for the potential-resolved multicolor ECL emission was proposed. Furthermore, the first ECL imaging sensing method was fabricated for the sensitive quantitative detection of rutin based on the effective quenching effect of rutin on the ECL of TiO2-NPs/g-C3N4. The linear response range is 0.005-400 µM with detection limit as low as 2 nM. This work presents a simple way to prepare g-C3N4-based nanocomposites with potential-resolved multicolor ECL, which broadens the potential applications of g-C3N4-based nanocomposites for ECL imaging sensing and light-emitting devices.

O-Fluorobenzoic Acid-Mediated Construction of Porous Graphitic Carbon Nitride with Nitrogen Defects for Multicolor Electrochemiluminescence Imaging Sensing.

Graphitic carbon nitride (g-CN) is an attractive electrochemiluminescence (ECL) luminophore. However, g-CN with wavelength-tunable ECL emission is still limited, which limits its application in multicolor ECL sensing and imaging analysis. In this study, porous g-CN (PCN) with nitrogen defects was synthesized through the condensation of melamine by using o-fluorobenzoic acid (o-FBA) as an effective regulation reagent. A series of PCNs, including PCN-5%, PCN-10%, and PCN-30%, were obtained by changing the mass ratio of o-FBA and melamine. The porous structure and tunable chemical composition change of the PCNs were carefully characterized. The nitrogen defects and porous structure of the synthesized PCNs can enlarge the specific surface area, facilitate electron transfer, and generate various surface states with gradually changed energy bands, leading to wavelength-tunable multicolor ECL emissions. Accordingly, g-CN, PCN-5%, PCN-10%, and PCN-30% can generate navy blue, turquoise blue, turquoise green, and olive green ECL emissions, respectively, with the peak ECL wavelength varied from 465 to 550 nm. Then, a multicolor ECL sensing array was proposed for the discrimination of polyphenols based on the prepared g-CN and PCNs by using a smartphone as a portable detector for the first time. Five polyphenol substances including vitamin P, resveratrol, phloretin, phlorizin, and caffeic acid were discriminated by using principal component analysis and hierarchical cluster analysis. The present work provides a simple strategy to adjust the ECL wavelength of g-CN and presents a simple way to fabricate multicolor ECL sensing array, which has great application potential for multiplexed analysis and multicolor ECL imaging sensing.

Multifunctionalized Hydrogel Beads for Label-Free Chemiluminescence Imaging Immunoassay of Acute Myocardial Infarction Biomarkers.

Hydrogel beads exhibit good biocompatibility, high stability, and monodispersity. However, hydrogel beads possessing intensive and multicolor chemiluminescence (CL) have not been reported. In this work, two kinds of multifunctionalized hydrogel beads, one consisting of chitosan (CS), Co2+, luminol, and gold nanoparticles (AuNPs) (CS-Co2+-Lu-Au), and another consisting of CS, Co2+, luminol, fluorescein, and AuNPs (CS-Co2+-Lu-FL-Au), were prepared via a facile synthesis method. The synthesized CS-Co2+-Lu-Au and CS-Co2+-Lu-FL-Au hydrogel beads exhibit high stability, simple operability, and can generate strong and uniform blue- and green-colored CL emission, respectively, when reacting with H2O2. Specific antibodies (Ab) can be assembled onto the surface of CS-Co2+-Lu-Au and CS-Co2+-Lu-FL-Au hydrogel beads directly via CS and surface-coated AuNPs as binding sites to obtain multifunctionalized hydrogel beads with both good CL activity and immunoactivity. Then, simple, fast, and versatile label-free CL imaging immunoassays were fabricated for the determination of two important acute myocardial infarction (AMI) biomarkers, including cardiac troponins I (cTnI) and heart-type fatty acid-binding protein (h-FABP), using a smartphone as a portable detector. The proposed CL imaging immunoassays using CS-Co2+-Lu-Au-Ab and CS-Co2+-Lu-FL-Au-Ab as sensing platforms can be carried out without complex instruments or time-consuming centrifugation or magnetic separation, greatly simplifying the assay procedures. The linear ranges for cTnI and h-FABP detection were 1.0 × 10-11 to 1.0 × 10-5 g/mL with detection limits as low as 1.57 and 1.61 pg/mL, respectively. Furthermore, the fabricated CL imaging immunoassays were successfully applied to determine cTnI and h-FABP in healthy human and patient serum samples, demonstrating their practicability in AMI diagnosis. The easy synthesis and versatility of the as-prepared CL hydrogel beads for the direct immobilization of Ab provide universal platforms for a wide range of CL immunoassays.

Microfluidic paper-based analytical device by using Pt nanoparticles as highly active peroxidase mimic for simultaneous detection of glucose and uric acid with use of a smartphone.

Herein, a simple microfluidic paper-based analytical device (µPAD) by using platinum nanoparticles (Pt NPs) as highly active peroxidase mimic for simultaneous determination of glucose and uric acid was fabricated. The µPAD consisted of one sample transportation layer, four paper-based detection chips, and two layers of hydrophobic polyethylene terephthalate (PET) films. The four detection chips were immobilized with various chromogenic reagents, Pt NPs, and specific oxidase (glucose oxidase or uricase). H2O2 generated by specific enzymatic reactions could oxidize co-immobilized chromogenic reagents to produce colored products by using Pt NPs as efficient catalyst. The multi-layered structure of µPAD could effectively improve the color uniformity and color intensity. Total color intensity from each two detection chips modified with distinct chromogenic reagents were used for quantitative analysis of glucose and uric acid, respectively, resulting in significantly improved sensitivity. The linear range for glucose and uric acid detection was 0.01-5.0 mM and 0.01-2.5 mM, respectively. Satisfied results were obtained for glucose and uric acid detection in real serum samples. An easy-to-use smartphone APP was developed for convenient and intelligent detection. The developed µPAD integrated with smartphone as detector holds great applicability for simple and portable on-site analysis.

Cobalt-imidazole metal-organic framework loaded with luminol for paper-based chemiluminescence detection of catechol with use of a smartphone.

Chemiluminescence (CL) reagent luminol was loaded into the porous structure of cobalt-imidazole metal-organic framework (MOF) ZIF-67 to obtain luminol-functionalized ZIF-67 (luminol@ZIF-67) with CL property. The morphology, composition, CL property, and CL mechanism of luminol@ZIF-67 were carefully investigated. The obtained luminol@ZIF-67 exhibited strong, stable, and visible CL emission that reacted with H2O2, attributed to the strong catalytic effect of ZIF-67 combined with the shortened diffusion distance between luminol and the catalytic center. The CL intensity of luminol@ZIF-67 was more than 550 times higher than that of luminol. Catechol can effectively quench the CL emission of luminol@ZIF-67 that reacted with H2O2. Then, a simple paper-based CL imaging detection method was developed for the detection of catechol by using a smartphone as a portable detector. The linear calibration curve of the developed CL assay for catechol ranged from 5 to 100 mg/L with detection limit of 1.1 mg/L (S/N = 3δ). The strong CL emission of luminol@ZIF-67 combined with the effective quench ability of catechol guaranteed high sensitivity of the detection method. The practical application ability of the developed CL assay was tested by the determination of catechol in tea and tap water samples, resulting in acceptable results. This work provides an effective paper-based CL detection method for catechol and enriches the species of the chemiluminescent MOF material.

ß-Cyclodextrin coated porous Pd@Au nanostructures with enhanced peroxidase-like activity for colorimetric and paper-based determination of glucose.

ß-cyclodextrin-functionalized porous Pd@Au nanostructures (ß-CD-Pd@Au) with intrinsic and enhanced peroxidase-like activity were successfully synthesized by a two-step method. The synthesized ß-CD-Pd@Au can efficiently catalyze the oxidation of various substrates, such as 3,3',5,5'-tetramethylbenzidine (TMB), mixture of 4-amino antipyrine (4-AAP) and 3,5-dichloro-2-hydroxy acid sodium (DHBS) (4-AAP/DHBS), and mixture of 4-AAP and N-Ethyl-N-(3-sulfopropyl)-3-methyl-aniline sodium salt (TOPS) (4-AAP/TOPS), by H2O2 to generate visual blue, purple, and pink color, respectively. The UV-vis absorbance peak of the three ß-CD-Pd@Au catalyzed the chromogenic reaction system located at 650 nm, 510 nm, and 550 nm, respectively. The ß-CD-Pd@Au-catalyzed TMB-H2O2 chromogenic reaction exhibited higher absorbance intensity, catalytic efficiency, and color stability in comparison to 4-AAP/DHBS-H2O2 and 4-AAP/TOPS-H2O2 chromogenic reactions. The catalytic activity of ß-CD-Pd@Au was enhanced about 4-fold compared to that of Pd@Au in terms of Kcat for H2O2. Using TMB as chromogenic substrate, a colorimetric assay was fabricated for the determination of H2O2 with a detection limit of 2.78 µM (absorbance at 650 nm). The colorimetric determination of glucose with a detection limit of 9.28 µM was further achieved by coupling with glucose oxidase enzymatic reaction, indicating the versatility of the ß-CD-Pd@Au-based detection strategy. A paper-based detection method coupled with smartphone for fast visual and instrument-free detection of glucose was further developed. Finally, the developed colorimetric assay and paper-based detection method were successfully applied to the determination of glucose in human serum sample. Graphical abstract.