Charge Neutralization Strategy to Construct Salt-Tolerant and Cell-Permeable Nanoprobes: Application in Ratiometric Sensing and Imaging of Intracellular pH

Abstract

Intracellular pH homeostasis is essential for the survival and function of biological cells. Negatively charged molecular probes, such as pyranine (HPTS), tend to exhibit poor salt tolerance and unsatisfactory cell permeability, limiting their widespread use in intracellular assays. Herein, we explored a charge neutralization strategy using multicharged cationic nanocarriers for an efficient and stable assembly with the pH-sensitive HPTS. Through immobilization and neutralization with poly-(allylamine hydrochloride)-stabilized red-emitting gold nanoclusters (PAH-AuNCs), the resulting nanoprobes (HPTS-PAH-AuNCs) offered improved salt tolerance, satisfactory cell permeability, and dual-emission properties. The fluorescence ratio exhibited a linear response over the pH range of 3.0−9.0. Moreover, the proposed HPTS-PAH-AuNCs were successfully applied to determine and visualize lysosomal pH variations in living cells, which indicated great potential for biosensing and bioimaging applications in living systems. Benefiting from the charge neutralization strategy, various types of probes can be expected to achieve broader analytical applications.

Facile construction of highly luminescent and biocompatible gold nanoclusters by shell rigidification for two-photon pH-edited cytoplasmic and in vivo imaging

“…After the incubation of PVP-AuNCs for 1 hour, cells were treated with high K + HEPES buffer in the presence of 5 μg mL −1 nigericin for 20 min. 37,38 As shown in Fig. 4(D), at pH 4.5 and 5.5, the cells exhibit negligible fluorescence; however, when the pH increases from 6.0 to 8.5, bright fluorescence is observed and gets stronger which is inconsistent with the phenomenon in solution, suggesting that the PVP-AuNCs are capable to respond to the change of pH in cells.…”

Cucurbit [8] uril-based supramolecular fluorescent biomaterials for cytotoxicity and imaging studies of kidney cells

“…Moreover, the significantly increased fluorescence signals of Q [8]@PEG-APTS were observed in cells incubated with 25 μM for 1 h compared to Frontiers in Chemistry frontiersin.org (HPTS), could be predominantly localized in the lysosome of lung cancer cells (Chowdhury et al, 2015). However, other researchers observed HPTS diffused in the cytosol of Hela cells and Chinese hamster ovary cells (Sen Mojumdar et al, 2013;Cao et al, 2021). Therefore, the different distribution of Q [8]@PEG-APTS in these two types of renal residual cells has been the prime novelty of this study and this property may be helpful to identify diverse cell types when tracing live cells in the kidney.…”

Metal Nanoclusters in Point-of-Care Sensing and Biosensing Applications

“…A linear response in the pH range between 3 and 9 was obtained. 169 Figure 2 represents the schematic of the proposed ratiometric strategy for pH sensing.…”

“…While at pH 7 both AuNCs and PAH represented a strong PL emission, their emission at lower and higher pH values is quenched individually. A linear response in the pH range between 3 and 9 was obtained Figure represents the schematic of the proposed ratiometric strategy for pH sensing.…”