Rhodamine capped gold nanoparticles for the detection of Cr³⁺ ion in living cells and water samples

Rhodamine capped gold nanoparticles (Rh6G-Au NPs) were synthesized by simple reduction method. The crystalline nature, morphology, elemental composition and chemical state of Rh6G-Au NPs were analyzed by X-ray diffraction (XRD), Scanning Electron Microscope (SEM), High Resolution Transmission Electron Microscope (HR-TEM), Energy Dispersive Spectroscopy (EDAX) and X-ray Photoelectron Spectroscopy (XPS). Aqueous solution of Rh6G-Au NPs exhibits an enhanced strong absorption and emission peak at 525 and 551 nm respectively, upon addition of Cr³⁺ ion. The sensing behavior of Rh6G-Au NPs toward Cr³⁺ ion was investigated by naked eye detection, absorption and fluorescence spectroscopy. The probe displayed an excellent selectivity for Cr³⁺ ions (K_a = 1.345 ×10⁴ M^-1 and limit of detection (LOD) = 9.28 µM) over other competing metal ions in water. In addition, probe which has 90% cell viability detects intracellular Cr³⁺ in the human breast cancer cells (HeLa) and articulated its value of practical applications in bioimaging. Further application of the probe as a detector of Cr³⁺ ions in different water samples was also evaluated.