A gold nanoparticle doped flexible substrate for microplastics SERS detection.

Due to overuse of plastic products, decomposed microplastics (MPs) are widely spread in aquatic ecosystems, and will cause irreparable harm to the human body through the food chain. Traditional MP detection methods require cumbersome sample pre-processing procedures and complex instruments, so there is an urgent demand to develop methods to achieve simple on-site detection. Herein, a simple, sensitive, accurate, and stable MP detection method based on surface-enhanced Raman scattering (SERS) is investigated. Considering the hydrophobic problems of MPs, gold nanoparticle (AuNP) doped filter paper as a flexible SERS substrate is applied to capture MPs in the fiber pores. Benefitting from the electromagnetic (EM) hot spots generated by AuNPs, the Raman signal of MPs can be effectively enhanced. Meanwhile, the flexible SERS substrate has good sensitivity to a minimum detectable concentration of 0.1 g L-1 for polyethylene terephthalate (PET) in water, and the maximum enhancement factor (EF) can reach 360.5. Furthermore, the practicability of the developed method has been proved by the successful detection of MPs in tap water and pond water. This research provides an easy process, high sensitivity, and good reproducibility method for MP detection.

Forced and natural convective drying of trehalose/water thin films: implication in the desiccation preservation of Mammalian cells.

Trehalose is believed to offer desiccation protection to mammalian cells by forming stable glassy matrices. The goal of the current study was to explore the desiccation kinetics of thin films of trehalose-water solution under forced and natural convective conditions and to investigate the thermophysical state of mammalian cells at the bottom of the thin film. We developed a finite difference model based on the mass and energy conservation equations coupled to the water transport model from the cells. The boundary conditions were obtained from correlations or experimental measurements and the Gordon-Taylor equation was used to predict the glass transition temperature at every location. Results indicated that there are three distinct regimes for drying for both forced and natural convection, characterized by the slope of the moisture content plot as a function of time. Our results also indicate that the surface of the solution reached the glassy state in less than 10 min for the Reynolds (forced) numbers explored and approximately 30 min for some Rayleigh (natural convective) numbers; however, significant water was trapped at this instant. Larger drying force hastened quicker glass formation but trapped more water. The numerical model was capable of predicting the drying kinetics for the dilute region accurately, but deviated while predicting the other regimes. Based on these experimental validations of the model, the osmotic response of different cells located at the bottom of the solution with orders of magnitude difference in their membrane permeability (Lp) was predicted. The results suggested that extracellular glass formed around cells at the bottom of a trehalose-water solution by the propagation of glass into the solution; however it takes more than an order of magnitude time (approximately 7 min to >100 min for forced convective drying) to remove sufficient water to form glass around cells from the time when the first surface glass is formed. This is attributed to low diffusivity of water through the glass. In addition, the water transport from the glassy matrix could be either diffusion or Lp limited. For diffusion-limited transport, lowering the film thickness at the beginning of drying by half almost lowers the drying time by an order of magnitude. In summary, the optimal design of convective desiccation protocols requires accounting for the size of the cell, their membrane permeability (Lp) and the starting thickness of the solution.