Background:Field effect transistors (FETs) are solid-state electrical devices with semiconductor channels through which charge carriers are able to migrate and generate current. FETs can be modified to allow for protein sensing by deployment of affinity elements (antibodies) as receptors on the semiconducting channel surface to create an immunologically modified FET (immunoFET). Binding of analyte to receptors causes modulation of FET (current) that is easily detectable, allowing for quantitative detection of unlabeled analytes. These FET design may be scalable to allow for real-time, point-of-care diagnostic use. Methods:AlGaN/GaN heterojunction FETs were modified with IgG antibodies specific to CXCL9 to create immunoFET sensors. The sensors were then exposed to CXCL9 in multiple buffers (PBS, murine serum, human urine) as well as appropriate controls. The baselines and changes in conductance were compared between the following samples:A) phosphate buffer, B) murine serum that was doped with human CXCL9 to a concentration of 100ng/ml, and C) human urine samples collected (blinded study) from transplant patients at the time of diagnostic renal transplant biopsy.

Results: We present the successful detection of the inflammatory chemokine CXCL9 in both murine serum (doped to a known concentration) and in human urine from a transplant patient using immunoFETs modified with anti-CXCL9 IgG. CXCL9 was detected in renal transplant urine in biologically relevant levels, and were correlate with rejection by renal biopsy.

Conclusion: The presented work demonstrates the feasibility of immunoFET sensor operation in physiologic buffers. These immunoFETs show the potential to provide real-time quantification and monitoring of inflammatory mediators, allowing for minimally invasive interrogation of graft status at the bedside. The present studies represent an early step in the translation of this technology to human clinical applications.

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