Detecting rare pathological cells is of obvious clinical significance. Sensitive and selective RGO-based electrochemical biosensors were developed and demonstrated in literature to detect cancer cells with over expressed nucleolin on plasma membrane (e.g. breast cancer cells and human cervical carcinoma cells), at a LOD of thousand cells per ml.
To avoid RGO aggregation and introduce more –COOH groups, 3,4,9,10-perylene tetracarboxylic acid (PTCA) was used as a composite with RGO. The nanocomposite was covalently functionalized with NH2-modified nucleolin-specific aptamers (oligonucleotides serving as highly selective antibodies) as the recognition element. The binding of cancer cells increases the electron transfer resistance by blocking the access of the redox probe ([Fe(CN)6] 3-/ 4-). Electrochemical detection in amperometry mode provides high temporal resolution (milliseconds). Therefore, it is suitable to detect dynamic cellular activities in real-time.
A RGO based sensor for detection of the real-time kinetics of oxygen release from human erythrocytes in response to NaNO2 stimulation has been shown. Two kinds of excellent mediators for O2 reduction, namely, laccase (Lac) and 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), were functionalized onto RGO sheets to form a Lac–ABTS–RGO hybrid electrode.
An O2 level as low as 10 mM can be detected by this hybrid electrode. Cellular release of reactive oxygen species (such as H2O2) is an early indicator for cytotoxic events and cellular disorders. A RGO based electrochemical sensor has been coupled with live human breast cancer cells (MCF-7) to detect triggered cellular release of H2O2 in real-time and with a LOD of 0.1 mM.
To construct the electrode, RGO sheets were first electro-phoretically deposited on the indium tin oxide (ITO) glass. This was followed by electro-deposition of Prussian blue (artificial H2O2 catalyst) and adsorption of extracellular matrix proteins (laminin) to promote cell adhesion. Ten layers of RGO–PB–laminin were formed on the ITO substrate using layer-by-layer deposition. In situ, real-time, sensitive, and quantitative detection of extracellular H2O2 release from live cells was demonstrated. Specifically, it was determined that, upon stimulation of phorbol-12-myristate-13-acetate (PMA, 5 mg ml-1), 1011 H2O2 molecules were released from a single MCF-7 cell over 25 s.
Extracted and edited from “Biological and chemical sensors based on graphene materials by Yuxin Liu, Xiaochen Dong and Peng Chen in Chemical Society Reviews, 2012″