Photo-Attachment of Biomolecules for Miniaturization on Wicking Si-Nanowire Platform

We demonstrated the surface functionalization of a highly three-dimensional, superhydrophilic wicking substrate using light to immobilize functional biomolecules for sensor or microarray applications. We showed here that the three-dimensional substrate was compatible with photo-attachment and the performance of functionalization was greatly improved due to both increased surface capacity and reduced substrate reflectivity. In addition, photo-attachment circumvents the problems induced by wicking effect that was typically encountered on superhydrophilic three-dimensional substrates, thus reducing the difficulty of producing miniaturized sites on such substrate. We have investigated various aspects of photo-attachment process on the nanowire substrate, including the role of different buffers, the effect of wavelength as well as how changing probe structure may affect the functionalization process. We demonstrated that substrate fabrication and functionalization can be achieved with processes compatible with microelectronics processes, hence reducing the cost of array fabrication. Such functionalization method coupled with the high capacity surface makes the substrate an ideal candidate for sensor or microarray for sensitive detection of target analytes.National University of Singapore (Graduate School for Integrative Sciences and Engineering scholarship)GLOBALFOUNDRIES Singapore Pte. Ltd.Singapore-MIT Allianc

Research on CMOS latchup in quarter micron technology

This research work focuses on exploring the process techniques used to improve latchup immunity especially for 0.25 urn CMOS devices and investigating the behaviour of the parasitic bipolar transistors as the n+/p+ spacing is scaled to the sub-0.25 pm regime.Master of Engineerin

Miniature single-mode fiber refractive index interferometer sensor based on high order cladding mode and core-offset

A miniature single-mode fiber (SMF) refractive index (RI) interferometer sensor based on high order cladding mode and core offset is presented. The sensor is fabricated by first splicing a very short SMF to another SMF with core-offset to induce cladding mode propagation along the short SMF. The end of the SMF will be melted into a rounded tip to excite the propagating cladding mode into higher order at reflection which creates large phase delay. High RI sensitivity of 1.24 × 10-4 refractive index unit (RIU) and 8.35 × 10-5 RIU for RIU of 1.3350 and 1.3845, are obtained, respectively, for the physical length of 690- μm sensor

Gallium-Doped Tin Oxide Nano-Cuboids for Improved Dye Sensitized Solar Cell

Tin dioxide (SnO2) is a potential candidate to replace conventional titanium dioxide (TiO2) in dye-sensitized solar cells (DSSCs) because of its wider bandgap and higher electron mobility. However, SnO2 suffers from low band edge that causes severe backflow of electrons towards electrolyte (charge recombination). Herein, we demonstrate that gallium (Ga) doping can increase the band edge of SnO2, and we show that DSSCs using a Ga-doped SnO2 nano-cuboids based photoanode offer improved open circuit potential (∼0.74 V), fill factor (∼73.7%), and power conversion efficiency (∼4.05%).ASTAR (Agency for Sci., Tech. and Research, S’pore)Accepted versio

Cavity ringdown refractive index sensor using photonic crystal fiber interferometer

A refractive index sensor is demonstrated by integrating a photonic crystal fiber (PCF) Mach–Zehnder interferometer (MZI) into a cavity ringdown loop for improved sensitivity. By splicing a short section of PCF between two single-mode fibers and collapsing air holes over a short region at two splicing point, a MZI will be formed. This is due to the coupling between core and cladding modes in the collapsed region. Through determining the decay constants of cavity ringdown curve under varying external refractive index, a minimum detectable refractive index of 7.8 × 10−5 RIU can be achieved

Design, simulation and characterization of wheatstone bridge structured metal thin film uncooled microbolometer

It is demonstrated for the first time that the Wheatstone bridge structured metal thin film resistive uncooled microbolometer (in short, WB-bolometer) provides promising temperature sensitivity. This paper describes the design, simulation, and characterization of WB-bolometer using titanium nitride (TiN) thin film as the infrared (IR) sensing material. TiN thin film is designed into four resistors which are connected to each other in Wheatstone bridge configuration. The resistance value of each resistor changes with different rates upon IR absorption, which can be attributed to the difference in their associated thermal conductance. As a result, the bridge output voltage varies in response to the absorbed IR power. Simulation was employed to compare and characterize different designs of WB-bolometer. It was found that design with two sensing elements has the optimum performance. The proposed WB-bolometer is also capable of operating at elevated temperatures (> 250 oC) due to its adjustable and small initial offset voltage with minimum associated noise.Published versio

Scaffold-mediated non-viral delivery platform for CRISPR/Cas9-based genome editing

Genome editing, especially via the simple and versatile type II CRISPR/Cas9 system, offers an effective avenue to precisely control cell fate, an important aspect of tissue regeneration. Unfortunately, most CRISPR/Cas9 non-viral delivery strategies only utilise micro-/nano-particle delivery methods. While these approaches provide reasonable genomic editing efficiencies, their systemic delivery may lead to undesirable off-target effects. For in vivo applications, a more localized and sustained delivery approach may be useful, particularly in the context of tissue regeneration. Here, we developed a scaffold that delivers the CRISPR/Cas9 components (i.e. single guide RNA (sgRNA) and Cas9 protein complexes) in a localized and non-viral manner. Specifically, using mussel-inspired bioadhesive coating, polyDOPA-melanin (pDOPA), we absorbed Cas9:sgRNA lipofectamine complexes onto bio-mimicking fiber scaffolds. To evaluate the genome-editing efficiency of this platform, U2OS.EGFP cells were used as the model cell type. pDOPA coating was essential in allowing Cas9:sgRNA lipofectamine complexes to adhere onto the scaffolds with a higher loading efficiency, while laminin coating was necessary for maintaining cell viability and proliferation on the pDOPA-coated fibers for effective gene editing (21.5% editing efficiency, p < 0.001). Importantly, U2OS.EGFP cells took up Cas9:sgRNA lipofectamine complexes directly from the scaffolds via reverse transfection. Overall, we demonstrate the efficacy of such fiber scaffolds in providing localized, sustained and non-viral delivery of Cas9:sgRNA complexes. Such genome editing scaffolds may find useful applications in tissue regeneration.Accepted versio

Sustained delivery of siRNA/mesoporous silica nanoparticle complexes from nanofiber scaffolds for long-term gene silencing

A low toxicity and efficient delivery system is needed to deliver small interfering RNAs (siRNA) in vitro and in vivo. The use of mesoporous silica nanoparticles (MSN) is becoming increasingly common due to its biocompatibility, tunable pore size and customizable properties. However, bolus delivery of siRNA/MSN complexes remains suboptimal, especially when a sustained and long-term administration is required. Here, we utilized electrospun scaffolds for sustained delivery of siRNA/MSN-PEI through surface adsorption and nanofiber encapsulation. As a proof-of-concept, we targeted collagen type I expression to modulate fibrous capsule formation. Surface adsorption of siRNA/MSN-PEI provided sustained availability of siRNA for at least 30 days in vitro. As compared to conventional bolus delivery, such scaffold-mediated transfection provided more effective gene silencing (p < 0.05). On the contrary, a longer sustained release was attained (at least 5 months) when siRNA/MSN-PEI complexes were encapsulated within the electrospun fibers. In vivo subcutaneous implantation and biodistribution analysis of these scaffolds revealed that siRNA remained localized up to ~290 m from the implants. Finally, a fibrous capsule reduction of ~45.8 % was observed after 4 weeks in vivo as compared to negative scrambled siRNA treatment. Taken together, these results demonstrate the efficacy of scaffold-mediated sustained delivery of siRNA/MSN-PEI for long-term non-viral gene silencing applications.ASTAR (Agency for Sci., Tech. and Research, S’pore)MOE (Min. of Education, S’pore)NMRC (Natl Medical Research Council, S’pore)Accepted versio

Surface roughness effect on copper–alumina adhesion

The surface roughness of the substrate itself could play an important role for the bonding at the interface. In this paper, a correlation of the surface roughness of a rigid alumina substrate and its 2D model of estimated surface area has been studied using Atomic Force Microscopy (AFM). With rougher surface, the adhesive strength between a deposited copper film and the alumina substrate is higher due to the larger contact area at the interface. For 99.99% pure copper–96% pure alumina, this effect can account for an adhesive strength increment of more than 50%.ASTAR (Agency for Sci., Tech. and Research, S’pore)Accepted versio

Nanoporous tin oxide photoelectrode prepared by electrochemical anodization in aqueous ammonia to improve performance of dye sensitized solar cell

In this work, a nanoporous thin film consisting of sieve-like tin oxide (SnO2) sheets was prepared by anodization of tin foil in aqueous ammonia and applied as a photoelectrode for dye-sensitized solar cell (DSSC). Compared to the conventional SnO2 nanoparticle-based photoelectrode, the anodized nanoporous SnO2 electrode offers higher short circuit current (6.85 vs. 3.64 mA/cm2) and open circuit voltage (0.56 vs. 0.51 V) due to better charge transportation and better suppression of charge recombination. Consequently, the power conversion efficiency of the DSSC equipped with the anodized SnO2 electrode is enhanced by 63%.Published versio