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In this study, the effects of AlN/GaN superlattice (SL) thickness on performances of AlGaN/GaN high electron mobility transistor (HEMT) heterostructure grown by metal-organic chemical vapor deposition on silicon is investigated. Stress in GaN is controlled by varying the total thickness of the AlN/GaN SL. Improved crystal quality and surface roughness accomplished with 2200 nm-thick AlN/GaN SL, leads to an increase in high electron mobility (1760 cm2 (V s)−1) as well as two-dimensional electron gas concentration (1.04 × 1013 cm−2). AlGaN/GaN metal–insulator-semiconductor HEMT (MIS-HEMT) fabricated on the heterostructure with SL buffer layer exhibits a significant improvement in maximum saturation current of 1100 ± 29 mA mm−1 at V GS = 0 V and a low on-resistance of 4.3 ± 0.15 Ω mm for the optimized AlN/GaN SL. The 2200 nm-thick AlN/GaN SL supports the growth of stress-free GaN heterostructure, which can reduce the insertion loss for sub-6 GHz radio frequency (RF) applications. This GaN HEMT structure based on SL buffer layer is suitable for low-frequency RF power applications.

The analysis of surface antigens on cells, especially red blood cells (RBCs), has attracted increasing attention due to the recognition of antigenic variation that can facilitate early diagnoses. This paper presents an alternative methodology to estimate the variation of surface antigen expressions using an optical cell-detachment technique to validate the binding of individual RBCs stuck on corresponding antibody-coated surfaces. The detachment tests were implemented by an optical tweezers with gradually decreasing laser powers associated with serial antibody dilutions. Then, the antigen expression variation was estimated based on the known antibody dilution folds. The B- and B3-types of RBCs were selected for the demonstration subjects. With the semi-quantitative analysis, the proposed methodology was successfully verified for evaluating the variation of the RBC surface antigen expressions. The analysis result shows good consistency with the literature’s findings.

AlGaN/GaN high electron mobility transistors (HEMTs) heterostructures are grown by metal-organic chemical vapor deposition on silicon-on-insulator (SOI) substrate and high-resistivity silicon (HR-Si) simultaneously to investigate the influence of substrate types on electrical and thermal characteristics. The AlGaN/GaN HEMT epitaxial structure grown on SOI achieved high electron mobility (1900 ± 19 cm2 (V s)−1) and high two-dimensional electron gas carrier concentration (9.1 ± 0.1 × 1012 cm−2). The GaN HEMT metal–insulator–semiconductor gate device fabricated on the structure grown on the SOI substrate exhibits higher saturation current and improved buffer breakdown voltage compared with devices fabricated on HR-Si substrate. In particular, SOI substrate helps to improve the thermal-sensitive strain of the GaN-based heterostructure and reduced defect density in the epitaxy, thereby improve the temperature-dependent on-resistance (R ON) and the dynamic R ON of the device.

The quantitative analysis of surface antigens on cells, especially red blood cells (RBCs), has attracted increasing attention due to the recognition of antigenic changes that can facilitate early diagnoses. This paper presents an alternative methodology developed using the optical cell-detachment technique to evaluate antibody-antigen interactions and quantitatively analyze the RBC surface antigen expression. RBC subtyping was used to verify the proposed detection principle based on a comparison of the bonding strengths between individual RBCs and antibody coatings. The bonding strengths were measured with serial antibody dilutions with gradually decreasing laser powers, for which a single cell was optically detached from the corresponding antibody-coated surface. With the quantitatively analysis, the proposed alternative methodology was verified as a highly sensitive technique for detecting antigen expression on the RBC surface.

A serviceable bioprobe is one of the important components for the development of microfluidic and lab-on-a-chip systems. In this paper, we report a novel bioprobe, fabricated by laser-induced cross-linking technology, for simple and direct screening of Gram-positive bacteria on a biochip. The AcmA′ protein is known to bind specifically to peptidoglycan (PG), which forms the thick outside layer of Gram-positive bacteria. Moreover, the AcmA′ protein has a much broader spectrum of bacterium types than do antibodies that are more specific to only one bacterium type, because the AcmA′ protein is a generic characteristic of Gram-positive bacteria. Green fluorescent protein (GFP) is generally used as a molecular marker. In this study, GFP was fused with the AcmA′ protein to act as an indicator to trace the AcmA′ binding activity on PG by green fluorescence. The GFP-AcmA′ protein was three-dimensionally structured by laser-induced cross-linking photochemistry technology to fabricate a bioprobe for capturing Gram-positive bacteria. Positive and negative tests on Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus and Streptococcus agalactiae were demonstrated, respectively. Screening is readily performed using optical microscopy observation. The experiments show that only Gram-positive bacteria were bound on the GFP-AcmA′ probes after minutes of incubation and phosphate buffered saline (PBS) rinsing. No binding was observed with the Gram-negative bacteria or with reference probes composed of neutral bovine serum albumin (BSA). Repeated experiments indicate that our bioprobes are reusable. Finally, a 3D wedge-shaped GFP-AcmA′ probe was demonstrated in a microfluidic channel. This study provides a novel platform for convenient Gram-positive bacteria screening that could potentially be used in lab-on-a-chip applications.

Measurements of optical tweezers forces on biological micro-objects can be used to develop innovative biodiagnostics methods. In the first part of this report, we present a new sensitive method to determine A, B, D types of red blood cells. Target antibodies are coated on glass surfaces. Optical forces needed to pull away RBC from the glass surface increase when RBC antigens interact with their corresponding antibodies. In this work, measurements of stripping optical forces are used to distinguish the major RBC types: group O Rh(+), group A Rh(+) and group B Rh(+). The sensitivity of the method is found to be at least 16-folds higher than the conventional agglutination method. In the second part of this report, we present an original way to measure in real time the wall thickness of bacteria that is one of the most important diagnostic parameters of bacteria drug resistance in hospital diagnostics. The optical tweezers force on a shell bacterium is proportional to its wall thickness. Experimentally, we determine the optical tweezers force applied on each bacteria family by measuring their escape velocity. Then, the wall thickness of shell bacteria can be obtained after calibrating with known bacteria parameters. The method has been successfully applied to indentify, from blind tests, Methicillinresistant Staphylococcus aureus (MRSA), including VSSA (NCTC 10442), VISA (Mu 50), and heto-VISA (Mu 3)

Correction for ‘Laser-induced cross-linking GFP-AcmA′ bioprobe for screening Gram-positive bacteria on a biochip’ by Chuen-Fu Lin et al., RSC Adv., 2014, 4, 62882–62887.