Nanodiamond surface as a photoluminescent pH sensor

Abstract

A systematic spectroscopic characterization of highly homogeneous water suspensions of ‘buckydiamonds’ comprising sp3 cubic nanodiamond (ND) core covered with disordered sp2 shell densely decorated with oxygen-containing groups demonstrates the excitation-wavelength-dependent photoluminescence (PL) given by at least four types of specific structures on the ND surface (hydroxyl, C=O containing ketones, carboxylic anhydrides, and carboxyl groups). PL properties of NDs suspensions possess concentration-dependent behavior revealing tendency of NDs to agglomerate. PL of NDs has been found to be strongly sensitive to pH of the environment in wide range of pH values, i.e., 2-11. We disclosed the mechanisms of pH sensitivity of the ‘buckydiamond’ and proved that it can serve as all-optical sensor of tiny pH variations suitable for further exploitation for pH sensing locally in the area where NDs have been delivered for any purpose, e.g., bioimaging or therapeutic needs.

Spatial Manipulation of Fluorescent Colloidal Nanodiamonds for Applications in Quantum Sensing

“…A similar mechanism works for detecting paramagnetic samples or free radicals in biological samples. [53][54][55] NDs can also be harnessed for localized nuclear magnetic resonance (NMR) measurements. This involves manipulating the NDs to bring them into proximity to the sample, enhancing the signal as the detectability of a few nuclei diminishes with distance.…”

“…Reproduced with permission. [ 65 ] Copyright 2023, IOP Publishing Ltd d) Top; Schematic of association between a nanodiamond and EGF receptor. Bright field image of C. elegans, bright field and selective imaging protocol image of the intestine of C. elegans, bottom (left to right), the circle shows the nanodiamond and orange line shows the outline of the intestine.…”

“…c) pH calibration curve by taking the photoluminescence ratio -COOH and -OH functionalized NDs. Reproduced with permission [65]. Copyright 2023, IOP Publishing Ltd d) Top; Schematic of association between a nanodiamond and EGF receptor.…”