Adsorption and desorption of lysozyme on thermosensitive nano-sized magnetic particles and its conformational changes

Introduction In recent years, there has been a great interest in the fabrication of stimuli responsive polymer microspheres for technological application and fundamental studies. These stimuli responsive smart and intelligent polymeric materials can respond in shape or volume changes to small external stimuli such as temperature, pH and ionic strength etc [1, 2]. Among these stimuli responsive polymers N-isopropylacrylamdie (PNIPAM) is the most widely studied thermosensitive polymer. It has a Lower Critical Solution Temperature (LCST) of 32C in water. It collapses and shrinks above the LCST and swells and expands below the LCST. Due to its well defined and reversible low critical solubility temperature, poly (Nisopropylacrylamide) (PNIPAM) has long been investigated as a versatile tool in biology. The technology can be applied to various aspects of biotechnology, for example enzyme immobilization [3, 4], cell sorting [5], drug delivery [6], and protein separation and purification [7, 8]. Many researchers used reversible thermosensitivity of N-isopropylacrylamide as adsorption desorption tool. Elaissari and Bourrel [9] reported adsorption of human serum albumin (HSA) on polystyrene core and PNIPAM shell by controlling pH and temperature as adsorption parameters. They observed the maximum amount of protein was adsorbed at the isoelectric point of the protein and the main driving force involved was hydrophobic interaction. However, no work on conformational changes was conducted. Desorption of proteins from interfaces depends essentially on the conditions under which they have been adsorbed. Norde and Favier [10] reported adsorption of BSA and LYZ on finely dispersed silica particles and they observed subsequent desorption of about (80-100)% in morpholine solution of pH 8.5. The result showed structural alternation of both BSA and LYZ upon adsorption on silica surface. Desorption of protein from the magnetic particles could be achieved by controlling various factors such as pH, temperature and ionic strength.