Silver nanoprism-mediated protein estimation—an ultrasensitive platform for rapid estimation of protein concentration

Estimation of protein concentration in the range of nanogram level (ng/ml) is a big challenge for conventional protein estimation methods. The highly dipole sensitive spectroscopic properties of Silver nanoprism (AgNPR) has been utilized to develop a rapid and highly sensitive method for the estimation of globular protein concentration at ng/ml (or ppb) range. We have applied a unique molecular doping approach to introduce protein in the interstitial space of the Ag fcc(111) crystal planes within AgNPR structure. The presence of the doped protein induces deformation in the crystal plane arrangement of AgNPR that results in a quantitative red shift of the dipole resonance peak (D-peak) of AgNPR under UV–vis spectroscopy. The proposed method allows detection of a protein concentration range of as low as 1–20 ng ml−1- that is better than the sensitivity limit of conventional protein estimation techniques. This method has been successfully applied for commonly used proteins like haemoglobin (Hb), Bovine serum albumin (BSA), Trypsin (TRYP) and Lysozyme (LYS) with a very low limit of detection (LOD) within 2–6 ng ml−1. The lowest LOD value was shown by Hb as 2.08 ng ml−1. The method has further been validated by measuring Casein concentration from milk with an accuracy of 99% and 95% recovery for the concentration of 3.1 and 31 ng ml−1 respectively. Transmission emission microscopy (TEM) images show that the doped protein has been found to alter the size and shape of the AgNPR as a function of the dopant concentration by creating systematic deformation. This method does not require any alteration of the reaction temperature and solely depends on the physical interaction of doped protein with its neighbouring crystal structure of the nanoplanar geometry.