Metal-Free Colorimetric Detection of Pyrophosphate Ions by Inhibitive Nanozymatic Carbon Dots

Abstract

The pyrophosphate ion (P 2 O 7 4− , PPi) plays a critical role in various biological processes and acts as an essential indicator for physiological mechanism investigations and disease control monitoring. However, most of the currently available approaches for PPi species detection for practical usage still lack appropriate indicator generation, straightforward detection requirements, and operation convenience. In this study, a highly sensitive and selective PPi detection approach via the use of nanozymatic carbon dots (CDs) is introduced. This strategy eliminates the common need for metal ions in the detection process, where a direct indicator− PPi interaction is adopted to provide straightforward signal reports, and importantly, through a green indicator preparation. The preparation of this nanozymatic CDs' indicator utilizes an aqueous solution refluxing, employing galactose and histidine as the precursor materials. The mild conditions of the solution refluxing produce fluorescent CDs exhibiting peroxidase-mimic properties, which can catalyze the ophenylenediamine oxidation under the presence of H 2 O 2 . The introduction of PPi species, interestingly, inhibits this process very efficiently, the extent of which can be colorimetrically monitored by the generated yellow product 2,3-diaminophenazine. Spectroscopic results point to CD surface functional groups' selective binding toward PPi species, which severely interferes with the electron transfer process in the enzymatic catalysis. Relying on this CD peroxidasemimetic property inhibition, sensitive and selective recognition of PPi reaches a detection limit of 4.29 nM, enabling practical usage in complex matrixes. Owing to the superior compatibility and high stability of nanozymatic CDs, they can also be inkjet-printed on paper-based devices to create a portable and convenient platform for PPi detection. Both the solution and the paper-device-based selective recognitions confirm this unique and robust metal-free inhibitive PPi detection, which is supported by a convenient green preparation of nanozymatic CDs.

Designing Sensing Devices Using Porous Composite Materials

“…For these devices, the use of composite materials is common, and is often performed in conjunction with supporting polymer backings to increase device robustness. On the other hand, the porosity of the paper substrate allows the material hydrophilicity to be modified through impregnation of hydrophobic substances, such as photoresist [24], wax [26][27][28], and polydimethylsiloxane [29]. These hydrophobic chemicals can penetrate into the paper substrate pores, rendering the affected areas hydrophobic.…”

“…(B) An improved bulk material-electrode interface design for a sponge-based piezoresistive sensor. Adapted with permission from[27,37].…”

“…(A) Fabrication process of a piezoresistive pressure sensor made by stacking multiple pieces of silver nanoparticles-poly(3,4-ethylenedioxythiophene) (AgNP-PEDOT)-paper composite material. (B) An improved bulk material-electrode interface design for a sponge-based piezoresistive sensor.Adapted with permission from[27,37].…”

Sensing and imaging of PPi in vivo using lanthanide-based second near-infrared luminescent probes

“…13 Fluorescence sensing and bioimaging techniques have become important approaches in biomedical applications because they can provide real-time information about the location and amount of the biomarkers. In recent years, various fluorescent probes have been prepared for PPi detection including organic probes, 14,15 quantum dots, 16,17 silver nanoclusters, 18 etc. Guo et al reported an organic fluorescent probe for in vivo Cu 2+ /PPi detection based on 7-substituted coumarin.…”

Affinity-Switchable Lateral Flow Assay

“…Furthermore, monitoring enzyme activities by using LFA test strips remains inaccessible with the current molecular binding approach, as the detection of enzyme activities would require the enzyme to have a chemical reaction with its corresponding substrate. Although many paper-based chromogenic dye methods have been reported for rapid analysis of small reactive molecules and enzymes, the chromogenic dyes must undergo clearly distinguishable color changes that can be displayed in an obvious and easy-to-interpret manner. − Typically, a change of color requires a significant shift in the concentration of the chromogenic dye to its product. In low analyte concentrations, many chromogenic dyes, e.g., Bodipy, carbon dots, and rhodamine, shows only subtle color changes, which may not be discernible to a nonexperienced user. − Comparatively, a test line observed against the white background membrane of the LFA test strip can give a clear and distinct band.…”