Sensitive and rapid Bradford and BCA protein assay by a common desktop scanner

Abstract

Introduction and Aim: The conventional method of protein quantification involves the need for a costly spectrophotometer which is a bulky and expensive instrument. Also, it requires a considerable quantity of protein which is often valuable or not affordable. In this communication, we report a sensitive image-based protein assay method overcoming the challenges faced by the conventional method. BCA and Bradford protein assay in a miniaturized form is carried out on a polypropylene micro-test plate (PPµTP) using only 1 µl of the precious protein solution in the nanogram range without the need for expensive equipment for quantification. Materials and Methods: In this procedure, after the assay reaction, the assay plate with a color solution is turned upside down for capturing images in a desktop scanner. The image is then quantified digitally by a color space using freely available Adobe Photoshop and Macbeth color calculator software. Results: Standard graphs made by the present image–based method agreeably correlate with the absorbance–based method carried out in a microtiter plate with a Pearson coefficient of 0.995178 and 0.981006 for BCA and Bradford assay respectively. A test protein quantified by this method shows an accuracy of 97%. Further, we have reduced the protein assay time to 75 s only by performing the assay on PPµTP by microwave irradiation. Conclusion: Image-based protein assay is also performed in an ultra-miniature assay plate (UAP) which requires only 1 µl of assay solution, reducing the detection limit further to the 10 femtogram/test zone. In short, image–based protein assay on PPµTP and UAP platforms could be an outstanding alternative either to spectrophotometric or paper–based protein assay.