Validation of galectin-7 using backscattering interferometry

15 Background: More than 60% of lung cancer patients are diagnosed with advanced disease due to a lack of early diagnosis tools. These patients are ineligible for surgical resection and have a poor prognosis. This situation could be avoided if we could quantify lung cancer specific biomarkers at sufficiently low concentrations, providing an indication of disease threat. Backscattering Inerferometry (BSI) is a label-free sensor with a simple optical train that is used to quantify biomarkers in complex matrices at picomolar to femtomolar levels. Here we demonstrate that BSI can enable lung cancer biomarker validation in complex, volume constrained samples and at detection limits significantly better than ELISA. Methods: A BSI dose response curve for Galectin-7 was constructed by incubating increasing concentrations (0-20 ng/mL) of recombinant galectin-7 with 100 ng/mL of polyclonal antibody. The samples were mixed at 300 RPM for 2 before being injected into the BSI instrument and measured in triplicate each day. All reagents used were obtained from a commercial ELISA kit. An ELISA dose response curve was similarly constructed using spiked serum and spiked plasma according to the manufacturer’s recommended procedure. Finally, 9 patient serum samples were quantified using BSI and ELISA for direct comparison of the two technologies. Results: BSI was used to quantify galectin-7 in spiked serum and patients samples. The lower limit of detection with standards was determined to be 0.5 ng/mL for ELISA in serum, 10 ng/mL for ELISA in plasma, and 0.04 ng/mL for BSI in serum. In the analysis of 9 patient serum samples, all were quantifiable using BSI, which enjoys low pg/mL detection limits, yet with ELISA only 5 samples contained a galectin-7 concentration high enough to be measured. In this small sample set there was a good correlation between disease state and galectin-7 concentration as measured by BSI. Conclusions: This study demonstrates that BSI is well-suited for biomarker detection and validation, having a greater dynamic operating range and much lower limits of detection than standard commercially available ELISA kits. Future work will focus on detecting other NSCLC biomarkers that are undetectable with currently available technology.