Development of Fluorescent Carbon Nanoparticle-Based Probes for Intracellular pH and Hypochlorite Sensing

Abstract

Acid-base and redox reactions are important mechanisms that affect the optical properties of fluorescent probes. Fluorescent carbon nanoparticles (CNPs) that possess tailored surface functionality enable a prompt response to regional stimuli, offering a useful platform for detection, sensing, and imaging. In this study, mPA CNPs were developed through one-pot hydrothermal reaction as a novel fluorescent probe (quantum yield = 10%) for pH and hypochlorite sensing. m-Phenylenediamine was chosen as the major component of CNPs for pH and hypochlorite responsiveness. Meanwhile, ascorbic acid with many oxygen-containing groups was introduced to generate favorable functionalities for improved water solubility and enhanced sensing response. Thus, the mPA CNPs could serve as a pH probe and a turn-off sensor toward hypochlorite at neutral pH through fluorescence change. The as-prepared mPA CNPs exhibited a linear fluorescence response over the pH ranges from pH 5.5 to 8.5 (R2 = 0.989), and over the concentration range of 0.125–1.25 μM for hypochlorite (R2 = 0.985). The detection limit (LOD) of hypochlorite was calculated to be 0.029 μM at neutral pH. The mPA CNPs were further applied to the cell imaging. The positively charged surface and nanoscale dimension of the mPA CNPs lead to their efficient intracellular delivery. The mPA CNPs were also successfully used for cell imaging and sensitive detection of hypochlorite as well as pH changes in biological systems. Given these desirable performances, the as-synthesized fluorescent mPA CNPs shows great potential as an optical probe for real-time pH and hypochlorite monitoring in living cells.

Electrochemically synthesized green fluorescent carbon dots for quantitation of hypochlorite and carbendazim

“…Among these tested chemical reagents, only hypochlorite caused the fluorescence quenching of CDs. We believed that this quenching was caused by the reaction between hypochlorite and the functional groups such as aromatic amines possessed on the surface of the CD [ 41 – 43 ]. As shown in Fig.…”

“…Based on the 3σ/S (where σ represents the standard deviation of the blank, and S represents the slope of the calibration curve), LOD was calculated to be 0.096 μM, which is lower than most probes (Table S2) ( https://www.jfda-online.com/journal/vol31/iss2/4/ ) [ 44 – 47 ]. Two linear regions are believed due to the oxidation of surface functional groups and core chemical bonds [ 43 ]. Having the advantages of stability, sensitivity, and selectivity, we further applied the CD probe for sensing of hypochlorite in real water samples.…”

Fluorescent carbon dots and noble metal nanoclusters for sensing applications: Minireview

“…[ 56,72 ] Use of several ligands and precursors have been suggested efficient for improving the optical properties and biological functions of C dots and MNCs. [ 43,72,102 ] In addition, doping of C dots with nitrogen/sulfur atoms and formation of multiple metals in the core and multishells on the core surface of MNCs have shown effective in tuning the optical properties of C dots [ 46,130 ] and MNCs, [ 70,131,132 ] respectively. Fluorescent nanoprobes coupled with magnetic nanoparticles have demonstrated great application prospects in separation and detection, enabling rapid recognition and sensitive detection of trace proteins in complex real samples.…”

“…Based on our finding, many strategies have been proposed for the preparation of C dots from mixtures of at least two precursors. [ 43 ] Through hydrothermal routes, wastes such as coffee grounds, used tea, and leaves can also be used to prepare C dots. For quantitation of hydrophobic analytes, it is inconvenient using hydrophilic C dots as the probe.…”

“…[ 110 ] For example, C dots synthesized from m‐phenylenediamine and ascorbic acid through a hydrothermal route were sensitive toward hypochlorite, with a linear range of 125 nM to 1.25 μM and LOD of 0.029 μM. [ 43 ] The strong oxidative nature of hypochlorite oxidized the surface quinoid imino groups in the as‐prepared C dots, leading to fluorescence quenching. Similarly, nitrite (NO 2 − ) ions were detected using C dots prepared from m‐phenylenediamine through its inducing formation of diazo bonds between the surface aromatic primary amino groups of the C dots.…”