Publication Type:

Journal Article


Nanotechnology, Volume 21, Number 5 (2010)



Adenocarcinoma cells, Amide linkages, Amides, article, Ascorbic acids, Atomic Force, atomic force microscopy, Au clusters, Au nanoclusters, Binding energy, Bio-conjugation, Body fluids, Bovine, bovine serum albumin, Bovine serum albumins, Cancer cells, Cancer detection, Cancer imaging, Cancer-targeting, Carcinoma cells, carrier protein, Carrier Proteins, Cell culture, Cell Line, Cell Surface, cell surface receptor, Cell Survival, cell viability, Chemical properties, chemistry, Cluster interactions, Controlled reduction, Electron, flow cytometry, Fluorescence, Fluorescence efficiency, fluorescence microscopy, folate binding protein, Folate receptor, folate-binding protein, folic acid, Folic acids, formazan, Formazans, Fourier Transform Infrared, Gold, human, Humans, Image clusters, In-vitro, Infrared devices, infrared spectroscopy, Ketones, Light, Luminescence, Luminescent Measurements, Medical imaging, metabolism, microscopy, Mouth Neoplasms, mouth tumor, MTT formazan, Nanoclusters


Molecular-receptor-targeted imaging of folate receptor positive oral carcinoma cells using folic-acid-conjugated fluorescent Au25 nanoclusters(Au NCs) is reported. Highly fluorescent Au25 clusters were synthesized by controlled reduction of Au+ ions, stabilized in bovine serum albumin(BSA), using a green-chemical reducing agent, ascorbic acid (vitamin-C). For targeted-imaging-based detection of cancer cells, the clusters were conjugated with folic acid(FA) through amide linkage with the BSA shell. The bioconjugated clusters show excellent stability over a wide range of pH from 4 to 14 and fluorescence efficiency of ∼5.7% at pH 7.4 in phosphate buffer saline(PBS), indicating effective protection of nanoclusters by serum albumin during the bioconjugation reaction and cell-cluster interaction. The nanoclusters were characterized for their physico-chemical properties, toxicity and cancer targeting efficacy in vitro. X-ray photoelectron spectroscopy(XPS) suggests binding energies correlating to metal Au4f7/2∼83.97eV and Au4f5/2∼87.768eV. Transmission electron microscopy and atomic force microscopy revealed the formation of individual nanoclusters of size ∼1nm and protein cluster aggregates of size ∼8nm. Photoluminescence studies show bright fluorescence with peak maximum at ∼674nm with the spectral profile covering the near-infrared(NIR) region, making it possible to image clusters at the 700-800nm emission window where the tissue absorption of light is minimum. The cell viability and reactive oxygen toxicity studies indicate the non-toxic nature of the Au clusters up to relatively higher concentrations of 500νgml-1. Receptor-targeted cancer detection using Au clusters is demonstrated on FR+ve oral squamous cell carcinoma (KB) and breast adenocarcinoma cell MCF-7, where the FA-conjugated Au25 clusters were found internalized in significantly higher concentrations compared to the negative control cell lines. This study demonstrates the potential of using non-toxic fluorescent Au nanoclusters for the targeted imaging of cancer. © IOP Publishing Ltd.


cited By 104

Cite this Research Publication

A. Retnakumari, Setua, S., Menon, D., Ravindran, P., Muhammed, H., Pradeep, T., Nair, S., and Koyakutty, M., “Molecular-receptor-specific, non-toxic, near-infrared-emitting Au cluster-protein nanoconjugates for targeted cancer imaging”, Nanotechnology, vol. 21, 2010.

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