High performance chemical & physical sensors based on functional micro/nano-structures for environmental and healthcare applications

Nanomaterials exhibit distinct physical and chemical properties, enabling their applications to physical and chemical sensors with high performances, low-power consumption and high density device integration. Our group is working on the design and fabrication of chemical (eg. gas molecules and ions) and physical (eg. strain, force, pressure and light) sensors based on functional nanoparticles, nanowires, nanotubes, and their hybrid nanocomposites.

Flexible and stretchable strain sensors by elastomer-nanomaterial composite: The demand for flexible and wearable electronic devices is rapidly increasing. Especially, highly stretchable and flexible strain sensors are very useful for the human motion detection towards healthcare applications [1]. We have developed highly flexible, stretchable, and sensitive strain sensors based on the nanocomposite of elastomeric polymers and one dimensional (1D) nanomaterials (eg. silver nanowires and carbon nanotubes) [2, 3]. These types of sensors provide high piezoresistivity and stretchability due to the percolation network of 1D nanomaterials and elastic properties of elastomeric matrix, respectively. Another type of stretchable strain sensor utilizes the reversible crack opening/closure of metal nanoparticle thin film [4]. The optimization of sensing performances of stretchable strain sensors has also been made using numerical simulation [5]. Furthermore, we also have developed 3D strain sensor using the conductive nanocomposite and electrical impedance tomography for multi-touch, 3D sensing [6].

Soft and highly sensitive force sensors by microporous elastomers and their composites with conductive nanomaterials: Recently, wearable and flexible force / pressure sensors become very promising in their potential applications in electronic skin, touch-based display, and soft robotics. We have developed highly sensitive and ultra-soft force sensors by using microporous elastomers as dielectric layers in the capacitive sensors [7] and microporous elastomer-conductive 1D nanomaterial composites as piezoresistive layers in the resistive sensors [8]. These multiscale approaches allow ultra-low detection limit, high sensitivity as well as wide working range of force detection. We believe that these sensors would be very useful for wearable human-machine interface as well as for healthcare applications.

[1] M. Amjadi, K-U. Kyung, I. Park, and M. Sitti, “Stretchable, skin-mountable, and wearable strain sensors and their potential applications: A review”, Advanced Functional Materials 26, 1678-1698, Mar 2016
[2] M. Amjadi, A. Pichitpajongkit, S. Lee, S. Ryu and I. Park, “Highly stretchable and sensitive strain sensor based on silver nanowire-elastomer nanocomposite”, ACS Nano 8, 5154-5163, Apr 2014
[3] M. Amjadi, Y. Yoon and I. Park, “Ultra-stretchable and skin-mountable strain sensors using CNTs-Ecoflex nanocomposite”, Nanotechnology 26, 375501, Aug 2015
[4] J. Lee, S. Kim, J. Lee, D. Yang, B.C. Park, S. Ryu and I. Park, “A stretchable strain sensor based on a metal nanoparticle thin film for human motion detection”, Nanoscale 6, 11932-11939, Aug 2014
[5] S. Lee, M. Amjadi, N. M. Pugno, I. Park, and S. Ryu,”Computational analysis of silver nanowires-elastomer nanocomposite based strain sensors”, AIP Advances 5, 117233, Nov 2015
[6] H. Lee, D. Kwon, J. Cho, I. Park, and J. Kim, “Soft nanocomposite based multi-point, multi-directional strain mapping sensor using anisotropic electrical impedance tomography”, Scientific Reports 7, 39837, Jan 2017
[7] D. Kwon, T. Lee, M. S. Kim, S. Kim, T.-S. Kim and I. Park, “Highly Sensitive, Flexible and Wearable Pressure Sensor Based on a Giant Piezocapacitive Effect of Three-Dimensional Microporous Elastomeric Dielectric Layer”, ACS Applied Materials & Interfaces 8, 16922-16931, Jun 2016
[8] M. Amjadi, M. S. Kim and I. Park, “Flexible and sensitive foot pad for sole distributed force detection”, Proceedings of 14th International Conference on Nanotechnology (IEEE-NANO 2014), 764-767, Aug 2014

Figure 1. Flexible and stretchable physical sensors based on functional micro/nano-structures: (1) silver nanowire-PDMS composite based stretchable strain sensor (I. Park, et al., ACS Nano 2014), (2) 3D strain mapping sensor using conductive nanocomposite and electrical impedance tomography method (I. Park, J. Kim, et al., Scientific Reports, 2017), and (3) soft and sensitive pressure sensor using microporous elastomer (I. Park, et al., ACS Appl. Mater. Inter. 2016)

Chemical sensors by top-down fabricated nanowire array:Top-down nanofabrication methods based on nanolithography and dry etching processes allow facile and controllable approach to fabricate highly integrated nanowire arrays as compared to bottom-up nanofabrication methods [9-12]. We realized silicon nanowire array sensors by top-down nanofabrication and used them for the real-time chemical sensing of pH, metal ions, and biomolecules. Also, top-down fabricated silicon nanowires could be further surface-modified with catalytic metal nanoparticles and utilized for the gas molecule detection. [13, 14]. Furthermore, we have developed a novel method for the low-cost, large-scale nanofabrication of silicon nanomesh structures using nanosphere lithography and utilized it for the room-temperature hydrogen detection [15].

Air environmental monitoring by functional 1D nanomaterials: We developed a novel method for the controlled synthesis and direct integration of 1D nanomaterials on electronic devices by using localized hydrothermal synthesis along Joule heated microelectrodes. This method could realize high performance sensors to gaseous species such as H2, H2S, NO2 and CO [16-18]. Similar approach can be applied to the surface modification of 1D nanomaterials to further enhance sensitivity, response time, and power consumption. Furthermore, by combining with microfluidics, we could realize the fabrication of array of heterogeneous nanomaterials for multiplexed gas sensor [19]. Also, low-temperature, liquid-phase reaction on 1D nanotemplates was employed to the fabrication of multi-metallic 1D nanostructures for highly sensitive gas sensors on flexible substrate [20, 21]. Furthermore, we have developed a high resolution patterning of electrospun metal oxide nanofibers using electrohydrodynamic (EHD) printing on MEMS microheater platform for the multiplexed gas sensor array application [22].

[9] I. Park, Z. Li, X. Li, A.P. Pisano, and R. S. Williams, “Towards silicon nanowire-based biochemical sensors for intracellular detection”, Biosensors and Bioelectronics 22, 2054-2070, Apr 2007
[10] I. Park, Z. Li, A.P. Pisano, and R.S. Williams, “Selective surface functionalization of silicon nanowires via nanoscale Joule heating”, Nano Letters 7, 3106-3111, Oct 2007
[11] I. Park, Z. Li, A. P. Pisano, and R.S. Williams, “Top-down fabricated silicon nanowire sensor for real-time chemical detection”, Nanotechnology 21, 015501, Jan 2010
[12] S. Choi, I. Park, Z. Hao, H-Y. Holman, and A. P. Pisano, “Quantitative studies of long-term stable, top-down fabricated silicon nanowire pH sensors”, Applied Physics A 107, 421-428, Jan 2012
[13] J.-H. Ahn, J. Yun, Y.-K. Choi, and I. Park, “Palladium nanoparticle decorated silicon nanowire field-effect transistor with side-gates for hydrogen gas detection”, Applied Physics Letters 104, 013508, Jan 2014
[14] J-H. Ahn, J. Yun, D-I. Moon, Y-K. Choi, and I. Park, “Self-heated silicon nanowires for high performance hydrogen gas detection”, Nanotechnology 26, 095501, Feb 2015
[15] M. Gao, M. Cho, H. Han, Y. Jung and I. Park, “Palladium-decorated silicon nanomesh fabricated by nanosphere lithography for high performance, room temperature hydrogen sensing”, Small 14, 1703691, Mar 2018 (Front Cover Article)
[16] D. Yang, D.H. Kim, S.H. Ko, A.P. Pisano, Z. Li, and I. Park, “Focused energy field (FEF) method for the localized synthesis and direct integration of 1D nanomaterials on microelectronic devices “, Advanced Materials 27, 1207-1215, Feb 2015 (Front Cover Article)
[17] D. Yang, M. K. Fuadi, K. Kang, D. Kim, Z. Li, and I. Park, “Multiplexed gas sensor based on heterogeneous metal oxide nanomaterial array enabled by localized liquid-phase reaction”, ACS Applied Materials and Interfaces 7, 10152-10161, May 2015
[18] D. Yang, K. Kang, D. Kim, Z. Li, and I. Park, “Fabrication of heterogeneous nanomaterial array by programmable heating and chemical supply within microfluidic platform”, Scientific Reports 5, 8149, Jan 2015
[19] I. Cho, K. Kang, D. Yang, J. Yun, and I. Park, “Localized liquid-phase synthesis of porous SnO2 nanotubes on MEMS platform for low power, high performance gas sensors”, ACS Applied Materials & Interfaces 9, 27111-27119, July 2017
[20] B-S. Choi, Y. W. Lee, S. W. Kang, J. W. Hong, J. Kim, and I. Park, and Sang Woo Han, “Multi-Metallic Alloy Nanotubes with Nanoporous Framework”, ACS Nano 6, 5659-5667, May 2012
[21] M. Lim, D. Kim, C-O. Park, Y. Lee, S-W. Han, Z. Li, R.S. Williams, and I. Park, “A new route towards ultra-sensitive, flexible chemical sensors: metal nanotubes by wet-chemical synthesis along sacrificial nanowire templates”, ACS Nano 6, 598-608, Dec 2011
[22] K. Kang, D. Yang, J. Park, S. Kim, I. Cho, H. Yang, M. Cho, S. Mousavi, K. Choi, and I. Park, “Micropatterning of metal oxide nanofibers by electrohydrodynamic (EHD) printing towards highly integrated and multiplexed gas sensor applications”, Sensors and Actuators B: Chemical 250, 574-583, Apr 2017

Figure 2. High performance chemical sensors based on nanomaterials: (1) silicon nanomesh sensor for room temperature hydrogen detection (I. Park, et al., Small 2018), (2) ZnO nanowire sensors for gas sensing (I. Park, et al., Advanced Materials 2015), (3) Low-power H2S sensor based on localized synthesis of 1D nanomaterials on MEMS platform (I. Park, et al., ACS Applied Materials and Interfaces 2017), and (4) multiplexed gas sensor array based on EHD printing of electrospun metal oxide nanofibers (I. Park, et al., Sensors and Actuators B: Chemical 2017)

Nanomaterial-integrated microfluidics for biological applications: 1D nanomaterials can be easily integrated within microfluidic devices by either in-situ or ex-situ synthesis. Unique geometry (i.e. high aspect ratio and sharp tip) and high mechanical stiffness of 1D nanomaterials in microfluidic channel can be used for the mechanical manipulation or lysis of biological cells. We have shown that mechanical cell lysis enabled by nanowire bundles provides much higher yields than conventional chemical lysis method [23, 24]. Also, we have proven that pneumatic actuation of nanowire-integrated membrane can transfer genes or biomolecules into the cells with high efficiency [25, 26]. Furthermore, we have developed new microfluidic biomolecule sensors based on quantum dot (QD) decorated nanowires [27].

Nanowire heater array for thermal manipulation of molecules:High density nanowire arrays fabricated by top-down nanofabrication method can be used not only for chemical/biological sensing but also for the manipulation and control of chemical and biological reactions in nanoscale spaces. Due to the small size and thermal capacity of nanowires, localized temperature field with extremely high thermal gradient (~2 K/nm) and fast heating/cooling speed (< 2 μs) can be achieved in nanoscale space. This capability can be utilized for the control of chemical reaction at selected locations in nanoscale space [28, 29]. Also, we have developed novel techniques for accurate temperature measurement of nanowire heaters by using the photoluminescence of locally deposited QDs [30].

Sensor integrated medical tools for in-situ tissue diagnosis: Biopsy is a critical process to diagnose suspicious (eg. cancerous) biological tissues that has to be performed before surgery. Currently, biopsy process is image-guided by computed tomography (CT) or ultrasound imaging, which do not provide high accuracy. We are currently developing novel biopsy needles integrated with multi-modal sensors such as electrical impedance, pH and glucose [31, 32]. Furthermore, we are developing a multiplexed thin film type sensor for pressure and temperature monitoring of biological tissues during radio frequency (RF) ablation procedure of tumors in order to prevent steam popping phenomena [33].

[23] J. Kim, Z. Li, and I. Park, “Direct synthesis and integration of functional nanostructures in microfluidic devices”, Lab on a Chip 11, 1946-1951, Apr 2011
[24] J. Kim, J. W. Hong, D. P. Kim, J. H. Shin, and I. Park, “Nanowire-integrated microfluidic devices for facile and reagent-free mechanical cell lysis”, Lab on a chip 12, 2914-2921, May 2012
[25] K. Kim, J. Kim, J. Choi, S. Bae, D. Kwon, I. Park, D. Kim and T. Seo, “Rapid, high-throughput and direct molecular beacon delivery to human cancer cells using a nanowire-incorporated and pneumatic pressure-driven microdevice”, Small 11, 6215, Oct 2015 (Inside Front Cover Article)
[26] S. Bae, S. Park, J. Kim, J. S. Choi, K. H. Kim, D. Kwon, E-S. Jin, I. Park, D. H. Kim and T. S. Seo, “Exogenous gene integration for microalgal cell transformation using a nanowire-incorporated microdevice”, ACS Applied Materials & Interfaces 7, 27554, Nov 2015
[27] J. Kim, S. Kwon, J-K. Park, and I. Park, “Quantum Dot-Based Immunoassay Enhanced by High-Density Vertical ZnO Nanowire Array”, Biosensors and Bioelectronics 55, 209-215, May 2014
[28] J. Yun, C. Y. Jin, J-H. Ahn, S. Jeon, and I. Park, “Self-heated silicon nanowire array: selective surface modification with catalytic nanoparticles by nanoscale Joule heating and its gas sensing applications”, Nanoscale 5, 6851-6856, May 2013
[29] C. Y. Jin, Z. Li, R. S. Williams, K-C. Lee, and I. Park, “Localized temperature and chemical reaction control in nanoscale space by nanowire array”, Nano Letters 11, 4818-4825, Oct 2011
[30] J. Yun, J. Ahn, B. Lee, D. Moon, Y. Choi, and I. Park*, “Temperature measurement of Joule heated silicon micro/nanowires using selectively decorated quantum dots”, Nanotechnology 27, 505705, Nov 2016
[31] S. Kim, J-H. Park, K. Kang, C-O. Park, and I. Park, “Direct metal micropatterning on needle-type structures towards bioimpedance and chemical sensing applications”, Journal of Micromechanics and Microengineering 25, 015002, Dec 2014
[32] J. Park, W. Choi, K. Kim, W. Jung, J. Seo and I. Park*, “Biopsy Needle Integrated with Electrical Impedance Sensing Microelectrode Array towards Real-time Needle Guidance and Tissue Discrimination”, Scientific Reports 8, 264, Jan 2018
[33] Y. Jeong, J. Park, K. Kim, and I. Park, “Ultrathin flexible pressure sensor based on microstructured polyimide/carbon nanotube composite film with wide pressure range and its biomedical application”, in review

Figure 3. Biochemical / medical sensors based on functional micro/nano-structures: (1) nanowire-integrated microfluidic device for mechanical cell lysis (I. Park, et al., Lab on a Chip 2012), (2) QD-decorated nanowires for biomolecule detection (I. Park, et al., Biosensors and Bioelectronics 2014), (3) impedance sensor integrated needles for smart biopsy (I. Park, et al., Scientific Reports 2017), and (4) nanowire integrated microfluidic device for smart molecular delivery into biological cells and their transformation (I. Park, T. Seo, et al., Small 2015)