This article reviews the applications of scanning electrochemical microscopy (SECM) with ultramicroelectrode (UME) as a probe for characterization and imaging of single living cells. The permeation of cell membranes of several redox species was quantitatively estimated from the SECM measurements of the species in the vicinity region of the cells. The rates for the oxygen generation by photosynthesis and the oxygen consumption by respiration were determined for the detailed analysis of localized oxygen concentration around single cells. The images for photosynthetic and respiration activities were obtained with SECM based on the oxygen reduction current. A dual‐microdisk electrode was used for simultaneous imaging based on electroactive species to characterize single cells.
The respiratory activity of collagen-embedded living cells was imaged by scanning electrochemical microscopy (SECM) with the objective to study anticancer drug sensitivity. Two kinds of cancer cells, the human erythroleukemia cell line (K562) and its adriamycin-resistant subline (K562/ADM), were immobilized at the array of microholes micromachined on a silicon wafer for comparative characterization of their sensitivity to the anticancer drug, ADM. The results obtained by the SECM method showed correspondence to a conventional colorimetric assay (SDI assay). Furthermore, since the SECM assay is based on the noninvasive measurement of the respiration activity, continuous monitoring of a dose response was possible.
A high-sensitivity immunoassay system with surface plasmon field-enhanced fluorescence spectrometry (SPFS) was constructed using a plastic sensor chip and then applied to the detection of total prostate-specific antigen (total PSA) and GalNAcβ1-4GlcNAc-linked prostate-specific antigen (LacdiNAc-PSA) in serum, to discriminate between prostate cancer (PC) and benign prostate hyperplasia (BPH). By using this automated SPFS immunoassay, the detection limit for total PSA in serum was as low as 0.04 pg/mL, and the dynamic range was estimated to be at least five digits. A two-step sandwich SPFS immunoassay for LacdiNAc-PSA was constructed using both the anti-PSA IgG antibody to capture PSA and Wisteria floribunda agglutinin (WFA) for the detection of LacdiNAc. The results of the LacdiNAc-PSA immunoassay with SPFS showed that the assay had a sensitivity of 20.0 pg/mL and permitted the specific distinction between PC and BPH within the PSA gray zone. These results suggested that high-sensitivity automated SPFS immunoassay systems might become a powerful tool for the diagnosis of PC and other diseases.
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