Rapid ultrasensitive detection platform for antimicrobial susceptibility testing.

Rapid detection and phenotyping of pathogenic microbes is critical for administration of effective antibiotic therapies and for impeding the spread of antibiotic resistance. Here, we present a novel platform, rapid ultrasensitive detector (RUSD), that utilizes the high reflectance coefficient at high incidence angles when light travels from low- to high-refractive-index media. RUSD leverages a principle that does not require complex manufacturing, labeling, or processing steps. Utilizing RUSD, we can detect extremely low cell densities (optical density [OD] ≥ 5 × 10-7) that correspond to approximately 20 bacterial cells or a single fungal cell in the detection volume, which is nearly 4 orders of magnitude more sensitive than standard OD methods. RUSD can measure minimum inhibitory concentrations (MICs) of commonly used antibiotics against gram-negative and gram-positive bacteria, including Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli, within 2 to 4 h. Here, we demonstrate that antibiotic susceptibility tests for several pathogens can rapidly be performed with RUSD using both small inoculum sizes (500 cells/mL) and larger inoculum sizes (5 × 105 cells/mL) used in standard antibiotic susceptibility tests. We anticipate that the RUSD system will be particularly useful for the cases in which antibiotic susceptibility tests have to be done with a limited number of bacterial cells that are available. Its compatibility with standard antibiotic susceptibility tests, simplicity, and low cost can make RUSD a viable and rapidly deployed diagnostic tool.

Enhanced photocurrent and dynamic response in vertically aligned In2S3/Ag core/shell nanorod array photoconductive devices.

Enhanced photocurrent values were achieved through a semiconductor-core/metal-shell nanorod array photoconductive device geometry. Vertically aligned indium sulfide (In2S3) nanorods were formed as the core by using glancing angle deposition technique (GLAD). A thin silver (Ag) layer is conformally coated around nanorods as the metallic shell through a high pressure sputter deposition method. This was followed by capping the nanorods with a metallic blanket layer of Ag film by utilizing a new small angle deposition technique combined with GLAD. Radial interface that was formed by the core/shell geometry provided an efficient charge carrier collection by shortening carrier transit times, which led to a superior photocurrent and gain. Thin metal shells around nanorods acted as a passivation layer to decrease surface states that cause prolonged carrier lifetimes and slow recovery of the photocurrent in nanorods. A combination of efficient carrier collection with surface passivation resulted in enhanced photocurrent and dynamic response at the same time in one device structure. In2S3 nanorod devices without the metal shell and with relatively thicker metal shell were also fabricated and characterized for comparison. In2S3 nanorods with thin metal shell showed the highest photosensitivity (photocurrent/dark current) response compared to two other designs. Microstructural, morphological, and electronic properties of the core/shell nanorods were used to explain the results observed.

High optical absorption of indium sulfide nanorod arrays formed by glancing angle deposition.

Indium(III) sulfide has recently attracted much attention due to its potential in optical sensors as a photoconducting material and in photovoltaic applications as a wide band gap material. On the other hand, optical absorption properties are key parameters in developing photosensitive photodetectors and efficient solar cells. In this work, we show that indium sulfide nanorod arrays produced by the glancing angle deposition technique have superior absorption and low reflectance properties compared to conventional flat thin film counterparts. We observed an optical absorption value of approximately 96% for nanorods at wavelengths <500 nm in contrast to 79% for conventional thin films of indium sulfide. A superior photoconductivity (PC) response as high as about 40% (change in resistance upon illumination) was also observed in nanorod samples. This is mainly believed to be due to their high optical absorption, whereas only less than 1% PC change was detected in conventional thin films. We give a preliminary description of the enhanced light absorption properties of the nanorods by using the Shirley-George model, which predicts diffusion of light as a function of the roughness of the surface.