Preparation of biodegradable polymer nanoparticles stabilized with the poly (vinyl alcohol)-sodium dodecyl sulfate mixture: Effect of the lactide/glycolide molar ratio

Abstract: This study examines the effects of the lactide/glycolide molar ratio on the synthesis of polymeric nanoparticles using a PVA-SDS stabiliser solution. PLA was obtained with a ratio of 100/0, while PLGA was synthesized at ratios of 88/12 and 64/36. Polymerizations employed ROP at 130°C with stannous octanoate and 1-dodecanol as catalysts. Polymerizations were conducted through ring opening at 130°C with stannous octanoate and 1-dodecanol as catalyst and co-catalyst. Characterized polymers were used to prepare emulsions stabilized with polyvinyl alcohol (15 g/L) alone or mixed with sodium dodecyl sulfate of various molecular weights (MW=13-23, 31-50 and 85-124 KDa). These emulsions were stored in phosphate-buffered saline for 28 days at 37.4°C. Colloidally stable emulsions were achieved using different poly (vinyl alcohol) concentrations, with the lactide/glycolide molar ratio influencing particle diameter. The electrostatic stabilizer formed by the poly (vinyl alcohol)-sodium dodecyl sulfate mixture demonstrated .Superior stabilization compared to poly (vinyl alcohol) alone, representing a novel finding. Moreover, the poly (vinyl alcohol-sodium dodecyl sulfate) mixture showed reduced water diffusion into the nanoparticles compared to poly (vinyl alcohol) alone, as evidenced by molecular weight and pH measurements. Additionally, the degradation of poly (lactic acid) and poly (lactic-co-glycolic acid) films was investigated; pH measurements in the immersed solutions showed that the degradation was increased with higher glycolide content

A Large Response Range Reflectometric Urea Biosensor Made from Silica-Gel Nanoparticles

A new silica-gel nanospheres (SiO2NPs) composition was formulated, followed by biochemical surface functionalization to examine its potential in urea biosensor development. The SiO2NPs were basically synthesized based on sol–gel chemistry using a modified Stober method. The SiO2NPs surfaces were modified with amine (-NH2) functional groups for urease immobilization in the presence of glutaric acid (GA) cross-linker. The chromoionophore pH-sensitive dye ETH 5294 was physically adsorbed on the functionalized SiO2NPs as pH transducer. The immobilized urease determined urea concentration reflectometrically based on the colour change of the immobilized chromoionophore as a result of the enzymatic hydrolysis of urea. The pH changes on the biosensor due to the catalytic enzyme reaction of immobilized urease were found to correlate with the urea concentrations over a linear response range of 50–500 mM (R2 = 0.96) with a detection limit of 10 mM urea. The biosensor response time was 9 min with reproducibility of less than 10% relative standard deviation (RSD). This optical urea biosensor did not show interferences by Na+, K+, Mg2+ and NH4+ ions. The biosensor performance has been validated using urine samples in comparison with a non-enzymatic method based on the use of p-dimethylaminobenzaldehyde (DMAB) reagent and demonstrated a good correlation between the two different methods (R2 = 0.996 and regression slope of 1.0307). The SiO2NPs-based reflectometric urea biosensor showed improved dynamic linear response range when compared to other nanoparticle-based optical urea biosensors

A Urea Biosensor from Stacked Sol-Gel Films with Immobilized Nile Blue Chromoionophore and Urease Enzyme

An optical urea biosensor was fabricated by stacking several layers of sol-gelfilms. The stacking of the sol-gel films allowed the immobilization of a Nile Bluechromoionophore (ETH 5294) and urease enzyme separately without the need of anychemical attachment procedure. The absorbance response of the biosensor was monitoredat 550 nm, i.e. the deprotonation of the chromoionophore. This multi-layer sol-gel filmformat enabled higher enzyme loading in the biosensor to be achieved. The urea opticalbiosensor constructed from three layers of sol-gel films that contained urease demonstrateda much wider linear response range of up to 100 mM urea when compared with biosensorsthat constructed from 1-2 layers of films. Analysis of urea in urine samples with thisoptical urea biosensor yielded results similar to that determined by a spectrophotometricmethod using the reagent p-dimethylaminobenzaldehyde (R2 = 0.982, n = 6). The averagerecovery of urea from urine samples using this urea biosensor is approximately 103%

A Urea Biosensor from Stacked Sol-Gel Films with Immobilized Nile Blue Chromoionophore and Urease Enzyme

An optical urea biosensor was fabricated by stacking several layers of sol-gelfilms. The stacking of the sol-gel films allowed the immobilization of a Nile Bluechromoionophore (ETH 5294) and urease enzyme separately without the need of anychemical attachment procedure. The absorbance response of the biosensor was monitoredat 550 nm, i.e. the deprotonation of the chromoionophore. This multi-layer sol-gel filmformat enabled higher enzyme loading in the biosensor to be achieved. The urea opticalbiosensor constructed from three layers of sol-gel films that contained urease demonstrateda much wider linear response range of up to 100 mM urea when compared with biosensorsthat constructed from 1-2 layers of films. Analysis of urea in urine samples with thisoptical urea biosensor yielded results similar to that determined by a spectrophotometricmethod using the reagent p-dimethylaminobenzaldehyde (R2 = 0.982, n = 6). The averagerecovery of urea from urine samples using this urea biosensor is approximately 103%