Interface engineering with self-assembling Au@Ag@β-cyclodextrin bimetal nanoparticles to fabricate ring-like arrayed SERS substrate for sensitive recognition of phthalate esters based on host-guest interaction and the coffee ring effect

Herein, the Au@Ag@β-cyclodextrin (CD) nanoparticles with relatively uniform shape and size at ～13 nm in diameter have been successfully synthesized, the surface of the synthesized nanoparticles is evenly coated by...

Determination of Time of Death Based on Blood Ring Formation and RNA Degradation

Time of death (TOD) determination is crucial in criminal cases. The method used to determine the TOD so far is only based on the state of the corpse found, therefore a new method is needed to improve the accuracy of the TOD determination. This study aims to determine the TOD based on a new method, namely the formation of blood rings and RNA degradation. Blood is commonly found in crime scenes. Blood consists of liquid part that is plasma and cellular part consisting of erythrocytes, leukocyte, and thrombocytes. The composition of blood as a liquid that contains dissolved solids makes the drops of dried blood forming “coffee ring effect”, which is a ring-like form on the perimeter of a blood drop. Coffee ring effect is used as an indicator of time by looking at the thickness of the ring formed from the perimeter of the blood drop to the middle which increases with time. RNA degradation was observed using Peptidylprolyl isomerase A (PPIA) gene. The PPIA gene is found in leukocyte and is used to see the degradation of RNA per 30 minutes period using the RT-PCR and qPCR methods. Degradation was observed by comparing the cycle threshold (ct) value of the standard curve with the ct value of the samples per unit time. TOD could be determined by the percentage of the blood ring thickness up until 120th minutes, and by observing the degradation of RNA until the 60th minute, after that the RNA had completely degraded.

Evaporation-Induced Crystal Nucleation and Morphology of Dried Poly(Vinylidene Fluoride) Droplets

The evaporation of a polymer solution droplet is important in solution-based polymer film fabrications, such as inkjet printing, spray coatings, and droplet casting, etc. In this work, we investigated the effect of droplet size, solvent evaporation rate, and concentration on the “coffee-ring” effect, crystal nucleation, polymorphism, and morphology of dried poly (vinylidene fluoride) (PVDF) solution droplets with the atomic force microscopy (AFM) and two-dimensional grazing incidence wide angle X-ray scattering (2D GIWAXS) method. We found that the crystal structure, morphology and crystal distribution in the center and edge regions of dried PVDF droplets were different due to the “coffee-ring” effect. The “coffee-ring” effect of dried PVDF droplets was mainly composited of accumulated crystals at the edge region of a droplet, which was mainly made by the crystallization of migrated chains. The interplay between the migration of chains and the crystallization and solidification of PVDF droplets significantly influenced the formation of the “coffee-ring”. In addition, our results showed that the decrease in droplet size and the controlling solvent evaporation rate were effective ways to improve the electroactive crystalline phases (β and γ-phases) nucleation and decrease the crystal size.

Fully Printed High-Performance n-Type Metal Oxide Thin-Film Transistors Utilizing Coffee-Ring Effect

Metal oxide thin-films transistors (TFTs) produced from solution-based printing techniques can lead to large-area electronics with low cost. However, the performance of current printed devices is inferior to those from vacuum-based methods due to poor film uniformity induced by the “coffee-ring” effect. Here, we report a novel approach to print high-performance indium tin oxide (ITO)-based TFTs and logic inverters by taking advantage of such notorious effect. ITO has high electrical conductivity and is generally used as an electrode material. However, by reducing the film thickness down to nanometers scale, the carrier concentration of ITO can be effectively reduced to enable new applications as active channels in transistors. The ultrathin (~10-nm-thick) ITO film in the center of the coffee-ring worked as semiconducting channels, while the thick ITO ridges (>18-nm-thick) served as the contact electrodes. The fully inkjet-printed ITO TFTs exhibited a high saturation mobility of 34.9 cm2 V−1 s−1 and a low subthreshold swing of 105 mV dec−1. In addition, the devices exhibited excellent electrical stability under positive bias illumination stress (PBIS, ΔVth = 0.31 V) and negative bias illuminaiton stress (NBIS, ΔVth = −0.29 V) after 10,000 s voltage bias tests. More remarkably, fully printed n-type metal–oxide–semiconductor (NMOS) inverter based on ITO TFTs exhibited an extremely high gain of 181 at a low-supply voltage of 3 V, promising for advanced electronics applications.