Two‐Color Emitting Colloidal Nanocrystals as Single‐Particle Ratiometric Probes of Intracellular pH

Abstract

Intracellular pH is a key parameter in many biological mechanisms and cell metabolism and is used to detect and monitor cancer formation and brain or heart diseases. pH‐sensing is typically performed by fluorescence microscopy using pH‐responsive dyes. Accuracy is limited by the need for quantifying the absolute emission intensity in living biological samples. An alternative with a higher sensitivity and precision uses probes with a ratiometric response arising from the different pH‐sensitivity of two emission channels of a single emitter. Current ratiometric probes are complex constructs suffering from instability and cross‐readout due to their broad emission spectra. Here, we overcome such limitations using a single‐particle ratiometric pH probe based on dot‐in‐bulk CdSe/CdS nanocrystals (NCs). These nanostructures feature two fully‐separated narrow emissions with different pH sensitivity arising from radiative recombination of core‐ and shell‐localized excitons. The core emission is nearly independent of the pH, whereas the shell luminescence increases in the 3–11 pH range, resulting in a cross‐readout‐free ratiometric response as strong as 600%. In vitro microscopy demonstrates that the ratiometric response in biologic media resembles the precalibralation curve obtained through far‐field titration experiments. The NCs show good biocompatibility, enabling us to monitor in real‐time the pH in living cells.

Photocatalytic Activity of Polymer Nanoparticles Modulates Intracellular Calcium Dynamics and Reactive Oxygen Species in HEK-293 Cells

“…Although there are many studies on surface functionalization being carried out, the cytotoxicity of QDs still remains an issue, halting their possible biomedical applications (Medintz et al, 2005 ). Despite this, they offer a strongly selective and sensitive tool for biosensing (Howes et al, 2014 ) and fluorescence imaging (Bruni et al, 2017 ). The plasmonic resonance of metallic nanoparticles has been also successfully exploited to gain efficient photo-thermal processes upon NIR radiation (Yang et al, 2017 ), but in this case high photo-excitation densities are usually required.…”

Tailoring the Heterostructure of Colloidal Quantum Dots for Ratiometric Optical Nanothermometry

“…[75] Thus, when using QDs , the performance of the thermal sensor can be optimized by tuning the size/shape/chemical composition of the QDs, the surface structure/ligands of QDs, the electron-hole wave function in heterostructured QDs, selecting different semiconducting materials with different thermal expansion coefficient, ET in doped QDs, etc. [31,34,35,72,74,75] In QD-based optical nanothermometry, at least one emission band should be very sensitive to the temperature. For example, in the core/shell QDs or core/shell/shell QDs, both core and shell materials should have different emission windows and different thermal expansion coefficient.…”

“…Partially indirect recombination is usually found in the core/thick-shell QDs. [33,34,45,104,107,[118][119][120][121][122] As the shell is very thick, the exciton (e-h pair) photoexcited in the shell materials still has the probability to recombine within the shell, leading to an additional emission band in the core/thick-shell QDs. [33,45,118,120,121] These findings suggest the importance of controlling the double emission of core/thick-shell QDs by tuning the shell thickness and shape of the shell materials.…”

Kinetic and spectroscopic responses of pH-sensitive nanoparticles: influence of the silica matrix

“…69 Furthermore, the fairly high intensity change upon pH changes simplies the subsequent analyses and can be, at least partially, traced back to the smaller size as compared to other nanoparticle preparations. 31,[34][35][36]85 In addition, the particles consist of hardly toxic components and are smaller than most well-known nanoprobes. Therefore, our particles are ideally suited to track the intracellular pH in living cells as exemplied in live-cellular microscopy.…”