Cytokine assay on a cellular chip by combining collagen gel embedded culture with scanning electrochemical microscopy

A novel cytokine assay has been designed using a cellular chip by combining a collagen gel embedded cell culture technique with scanning electrochemical microscopy-enzyme linked immunosorbent assay (SECM-ELISA). An array of cell-collagen gel mixture (2 μL) was spotted on an antibody-coated chip and incubated for 0.5-24 h. The very small trace amounts of cytokines produced by the activated leukocytes on the chip were effectively entrapped within the collagen gel matrix, and these were collected with the immobilized antibodies on the chip. The chip was further treated with horseradish peroxidase (HRP)-labeled antibodies via the sandwich method after removing the cell-collagen gel spots from the chip. Scanning electrochemical microscopy (SECM) was used to quantitatively evaluate the cytokines from the activated leukocytes produced on the chip, and the SECM images were obtained to visualize the position and concentration of IL-1β secreted from THP-1 and HL-60 cell lines at concentration levels of 10-350 pg mL−1. Based on the chemiluminescence method, the sensitivity of the cytokine assay system in combination with SECM-ELISA is comparable to that of the marketed cytokine assay kit; further, the sample volume required for a single assay is drastically reduced.