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5 - Tunable Liquid Lenses
- from Part II - Devices and materials
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- By J. Andrew Yeh, National Tsing Hua University, Taiwan, Yen-Sheng Lu, National Tsing Hua University, Taiwan
- Edited by Hans Zappe, Albert-Ludwigs-Universität Freiburg, Germany, Claudia Duppé, Albert-Ludwigs-Universität Freiburg, Germany
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- Book:
- Tunable Micro-optics
- Published online:
- 05 December 2015
- Print publication:
- 17 December 2015, pp 123-155
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Summary
Introduction
Microlenses are used in many applications including optical coupling, light shaping, spatial light illumination modulation, and imaging (biomedical or monitoring). The basic function of a lens is to either diverge or converge the incident light beams. Solid lenses are the most widely used and have a fixed and nontunable focal length. In a solid lens module, voice coil motors (VCMs) are used to provide a back-and-forth track movement along the optical axis to achieve the required focal length change. However, the bulkiness and high power consumption of the lens module make it unsuitable for designing portable and energy saving products. The focal length of liquid lenses can be tuned by changing either the refractive index or the liquid lens geometry. As liquid lenses do not need any mechanical tracking devices such as VCMs for focal length tuning, the lenses provide the optimal solution for developing miniaturized lens modules with low power consumption in the mW range.
In the past two decades, liquid lenses have been widely investigated benefitting from the development of microfluidics (Berge & Peseux 2000, Chang et al. 2012, Chen et al. 2004). In microfluidics, the control or guidance of liquid/analyst droplets is very significant; especially for lab-on-a-chip (LOC) or micro-total analysis systems (μTAS). LOCs are devices that integrate one or several laboratory functions on a small chip of only few square millimeters to a few square centimeters in size, where the manipulation and the guidance of the tiny amounts of liquids or droplets becomes more and more significant. Certain liquid control mechanisms, such as external pressure pumping, electrowetting, and dielectrophoresis, have been developed and widely used for liquid manipulation (Agarwal et al. 2004, Berge & Peseux 2000, Cheng & Yeh 2007). The technique developed for the manipulation of liquids in microfluidics can be used to change the surface profile and the refractive indices of liquid lenses.
A liquid lens refracts the incident light beams based on the presence of the gradient index in liquids or the change in surface profiles formed from the solid (membrane)–liquid, liquid–liquid, and gas–liquid interfaces. The working liquids in the lens chamber must be transparent in the visible range and should be stable for a wide temperature range. To achieve these goals, liquid crystals, water, mixed alcohols, or silicone oil have been used and investigated.
Detection of DNA Hybridization using Functionalized InN ISFETs
- Cheng-Yi Lin, Yen-Sheng Lu, Shih-Kang Peng, Shangjr Gwo, J. Yeh
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- Journal:
- MRS Online Proceedings Library Archive / Volume 1202 / 2009
- Published online by Cambridge University Press:
- 31 January 2011, 1202-I09-09
- Print publication:
- 2009
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Ultrathin (∼10 nm) InN ion sensitive field effect transistors (ISFETs) are functionalized by immobilized label-free oligonucleotide probes with 3-mercaptopropyltrimethoxysilane (MPTMS) through molecular vapor deposition (MVD) technique. This layer on the InN surface serves the function of selectively detecting the hybridization of complementary deoxyribonucleic acid (DNA). Using MVD technique to perform the gas-phase silanization of MPTMS provided a time-saving and simple method to reach 68° water contact angle after 1.5 h treatment. High resolution X-ray photoelectron spectroscopy (HRXPS) was employed to analyze the surface characteristics after functionalization. Modified probes DNA were covalently bonded to MPTMS-covered gate surface of InN ISFETs. And further hybridized with complementary DNA For a 12-mer oligonucleotide probe, a significant drain-source current decrease (∼ 6 μA) was observed for the hybridization with complementary DNA solution of 100 nM. In contrast, the noncomplementary DNA with single-base mismatch did not show obvious current changes. Functionalized ultrathin InN ISFETs for DNA sequence detection demonstrate the promise of biological sensing and genetic diagnosis applications.
pH and Biological Sensing of Ultrathin (10nm) InN Based ISFETs
- Yen-Sheng Lu, Cheng-Yi Lin, Yuh-Hwa Chang, Yu-Liang Hong, Shangjr Gwo, J.A Yeh
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- Journal:
- MRS Online Proceedings Library Archive / Volume 1202 / 2009
- Published online by Cambridge University Press:
- 31 January 2011, 1202-I06-04
- Print publication:
- 2009
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Ultrathin (∼10 nm) InN ion selective field effect transistors (ISFETs) show a current variation ratio of 3.5 % per pH decade with a response time of less than 10 s. When the ISFET is employed as an electrolyte FET, the current variation of 18 % was measured as the gate bias changes from zero to 0.3 V given a drain-source voltage of 0.1 V. The high current (resistance) variation ratio is attributed to the ultrathin epilayer and an unusual phenomenon of intrinsic strong electron accumulation on InN surface, which enables a chemical/biological sensor with high sensitivity and resolution and permits detection of a slight concentration variation of the electrolyte. The pH response measurement of 10-nm-thick InN ISFETs investigated was performed in an aqueous solution titrated with diluted NaOH and HCl. The Helmholtz potential built at the electrolyte-InN interface is governed by direct adsorption of H+ ions at the surface metal oxides, modulating the channel current of the InN ISFETs. The channel current monotonically decreases as the pH value of an aqueous solution increases from 2 to 10. The sensitivity and resolution were found to be 58.3 mV per decade and 0.02 pH change, respectively. Besides, the detection of DNA hybridization was further performed after the InN surface was modified with MPTMS and probe DNA. A complementary target DNA solution of 100 nM led to a current decrease of approximate 6 uA, corresponding to the current variation of 0.74 %. The hybridization between negatively charged complementary DNA and the immobilized probe DNA caused the depletion of carriers at the InN surface, suppressing the channel current. The functionalized InN ISFETs are suitable for genetic analysis in clinical diagnostics without any labeling reagent. Such an InN-based sensor is appealing in the regime of chemical and biological sensing applications.