A simple strategy for charge selective biopolymer sensing
Experimental Materials and methods: CTAB, SDS, BSA, and PS and SCMC were procured from Sigma-Aldrich chemicals co. CS and pyrene was purchased from Fluka. Procured polysaccharides SCMC and CS were in highly pure state (99 %). Water was obtained from a Milli-Q purification system. Required amount of protein was mixed in MQ water to keep concentration 0.5 % weight for all experiments. All sensing experiments pH was kept constant and maintained at 3 with 0.001 N HCl in the medium. pH has been
... ed only in pH selectivity control experimentation. Fluorescence Measurements. Fluorescence studies were performed to examine the microenvironment of tryptophan (present in protein molecule) in protein-surfactant system in presence and absence of polysaccharide. All fluorescence studies were performed using a Shimadzu 5301PC spectrophotometer at room temperature. The excitation wavelength was set at 280 nm (for tryptophan and tyrosine residue in protein) and emission spectra were measured from 300 to 600 nm. Slit widths for both (excitation and emission) were set at 10 nm and 10 nm for BSA and pepsin respectively. ζ-potential Measurements. All ζ-potential measurements were performed in ζ-potential analyzer (Zeta Plus) from Brookhaven Instruments Corporation (BIC) equipped with 25 mW He-Ne, 677 nm laser Electronic Supplementary Material (ESI) for Chemical Communications This journal is source. All samples were prepared in MIlli-Q water and sonicated for 30 minutes before using. The ζ-potential is calculated from the electrophoretic mobility of the charged particles. Measurements were carried out at room temperature and three duplicates were taken for each sample and then averaged. DLS Measurements. The hydrodynamic sizes of protein-surfactant suspensions in Milli-Q water with and without polysaccharide were measured. DLS measurements were performed on a Brookhaven Instrument (BI 2000) equipped with an autoorrelator (BI-9K) and goniometer (BI-200SM) with BIHV photo multiplier tube. An argon ion laser (LEXEL 95-2) operating at 488 nm was used as a light source. The beam was focused onto the sample cell (standard cylindrical 4.5 ml cuvettes) through a temperature-controlled chamber (the temperature was controlled within 23 ± 0.1 0 C). All experiments were done at a correlation time of 2 min. The measurements were carried out at 90 o . The available software records the autocorrelation of the intensity trace during the experiment. Once the autocorrelation data have been generated, the averaged translational diffusion coefficient of the protein samples is derived mathematically from the fitting parameter, the average decays rate, and scattering vector at a given angle of 90 o . The hydrodynamic radius, R H , is computed based on the Stokes-Einstein equation. Three measurements were taken for each system and then the average hydrodynamic radius was obtained. Turbidimetric Measurements. The turbidimetric measurements were performed using Perkin-Elmer Lambda 35 UV/vis spectrophotometer. A wavelength of 400 nm in the visible regime was selected to examine the formation of protein-surfactant complex in presence and absence of polysaccharide. All solutions were prepared in deionized water and mixed well before measurement. Experiments were carried out at room temperature and measurements were taken in transmittance (%T) to maximize the precision. Measurements were carried out on two or three sample solutions prepared at different times from the same materials (replicates).