Nanoscale Mingsong Wang , Chenglong Zhao , Xiaoyu Miao , Yanhui Zhao , Joseph Rufo , Yan Jun Liu , * Tony Jun Huang , * and Yuebing Zheng *
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www.MaterialsViews.com Plasmofl uidics Plasmofl uidics: Merging Light and Fluids at the Micro-/ Nanoscale Mingsong Wang , Chenglong Zhao , Xiaoyu Miao , Yanhui Zhao , Joseph Rufo , Yan Jun Liu , * Tony Jun Huang , * and Yuebing Zheng * From the Contents 1. Introduction ........................................ 4424 P lasmofl uidics is the synergistic integration of 2. Plasmon-Enhanced Functionalities plasmonics and micro/nanofl uidics in devices and in Microfl uidics ....................................4424 applications in order to enhance performance. There has been signifi cant progress in the emerging fi eld of 3. Microfl uidics-Enhanced Plasmonic plasmofl uidics in recent years. By utilizing the capability Devices ................................................ 4433 of plasmonics to manipulate light at the nanoscale, 4. Summary and Perspectives ..................4440 combined with the unique optical properties of fl uids and precise manipulation via micro/nanofl uidics, plasmofl uidic technologies enable innovations in lab-on- a-chip systems, reconfi gurable photonic devices, optical sensing, imaging, and spectroscopy. In this review article, the most recent advances in plasmofl uidics are examined and categorized into plasmon-enhanced functionalities in microfl uidics and microfl uidics-enhanced plasmonic devices. The former focuses on plasmonic manipulations of fl uids, bubbles, particles, biological cells, and molecules at the micro/nanoscale. The latter includes technological advances that apply microfl uidic principles to enable reconfi gurable plasmonic devices and performance- enhanced plasmonic sensors. The article is concluded with perspectives on the upcoming challenges, opportunities, and possible future directions of the emerging fi eld of plasmofl uidics. small 2015, 11, No. 35, 4423–4444 © 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.small-journal.com 4423 reviews www.MaterialsViews.com 1. Introduction as well as enabling novel applications such as “plasmofl uidic lenses” [ 36 ] and single-molecule detection platforms enabled by Plasmonics is a fi eld dedicated to the fundamental study and “plasmofl uidic chips”. [ 37 ] In this review article, we will share application of surface plasmons (SPs), which are the light- with you some of the most important works in this emerging coupled coherent oscillations of free electrons at the inter- fi eld. We envision that plasmofl uidics will push the bounda- faces of metals and dielectric materials. [ 1–3 ] The ability of ries of traditional engineering approaches and bridge the two SPs to manipulate light at the nanoscale leads to numerous research fi elds of plasmonics and microfl uidics. With much yet intriguing physical phenomena such as localized heating [ 4,5 ] to be explored, we hope that the recent advances outlined in and plasmon-induced transparency. [ 6–8 ] Although the under- this review article will inspire others in these fi elds to take lying mechanisms are quite simple, plasmonic structures innovative steps to explore novel plasmofl uidics combinations and devices can have broad applications [ 9–12 ] and have been that could have a lasting impact on the world. employed to solve many challenges that arise due to the dif- fraction limit of conventional optics. For example, surface plasmon resonance (SPR) sensors, which utilize the critical 2. Plasmon-Enhanced Functionalities excitation conditions of surface plasmon waves to detect in Microfl uidics molecular-scale interactions on metal surfaces, have been successfully commercialized and have become an essential Due to the unique optical, mechanical, and thermal proper- tool for characterizing and quantifying biomolecular inter- ties at the nanoscale, surface plasmons can enhance various actions. [ 13–15 ] Other notable inventions in the fi eld of plas- functionalities related to the manipulation of fl uids, bubbles, monics include “invisibility cloaking” materials that do not particles, cells, and molecules in microfl uidics. Precise manipu- exist in nature [ 16,17 ] and small “satellites” that have been lations of fl uids and biomaterials are essential to immunoas- used to investigate organelle structures inside of single says, cell-molecule interaction studies, DNA hybridization, cells. [ 18,19 ] catalysis, and drug delivery. [ 20,21,38,39 ] Light is an ideal energy The fusion of plasmonics and micro/nanofl uidics is by source since it can be controlled remotely and easily inte- no means accidental and offers exciting opportunities to grated with a variety of platforms via readily available optical advance both fi elds. Each fi eld possesses inherent strengths components. For example, optical tweezers employ focused and advantages that the other generally lacks. Plasmonic laser beams to provide mechanical forces that can be used to devices are capable of detecting chemical changes and precisely manipulate single cells, cellular organelles, or bio- binding events with single-molecule resolution, but lack a molecules with high spatial resolution. [ 40 ] After roughly three means of precisely delivering an analyte sample in a high- decades of evolution, using light to trap and manipulate throughput manner. [ 20,21 ] In contrast, micro/nanofl uidic devices are capable of the precise, high-throughput delivery of fl uids, but lack the ability to simultaneously perform highly M. S. Wang, Prof. Y. B. Zheng sensitive measurements. These problems can be solved by a Department of Mechanical Engineering “plasmofl uidic” approach, which leverages the strengths and Materials Science and Engineering Program advantages of plasmonics and micro/nanofl uidics. Since the Texas Materials Institute integration of plasmonics with nanofl uidics is an emerging The University of Texas at Austin Austin , Texas 78712 , USA frontier that has only begun to be explored, in this review E-mail: [email protected] article, we will focus on the integration of plasmonics and Prof. C. L. Zhao microfl uidics. By analyzing recent trends in the fi elds of plas- Department of Physics monics and microfl uidics, it can be seen that the crossover Electro-Optics Graduate Program between the two fi elds has already started. Some plasmonic University of Dayton effects, such as the propagating surface plasmon polaritons Dayton, Ohio 45469 , USA (SPPs) and localized surface plasmon resonances (LSPRs), Dr. X. Y. Miao have already led to commercialized SPR sensors and micro- Google, Inc. fl uidic surface-enhanced Raman spectroscopy (SERS) for the 1600 Amphitheatre Pkwy , Mountain View, CA 94043 , USA clinical detection and diagnosis of numerous solution-based Y. H. Zhao, J. Rufo, Prof. T. J. Huang analytes. [ 22 ] Department of Engineering Science and Mechanics Department of Biomedical Engineering The success of “optofl uidics”, which synergistically com- Materials Research Institute bines microfl uidics with optics, sets an excellent precedent for Huck Institute of Life Sciences [ 23–31 ] the development of “plasmofl uidics”. With major efforts The Pennsylvania State University towards developing miniaturized on-chip imaging systems and University Park , Pennsylvania 16802 , USA fl uidic devices that manipulate light at the microscale, optofl u- E-mail: [email protected] idics broke down the barrier between microfl uidics and con- Dr. Y. J. Liu ventional optics, making it possible for the invention of devices Institute of Materials Research and Engineering and systems such as “on-chip fl ow cytometers” [ 32,33 ] and “cell- Agency for Science, Technology and Research (A*STAR) 3 Research Link , Singapore 117602 , Singapore phone microscopes”. [ 34,35 ] With its ability to extend conven- E-mail: [email protected] tional optics into nanoscale regimes, “plasmofl uidics” provides excellent opportunities for exploring new physical phenomena DOI: 10.1002/smll.201500970 4424 www.small-journal.com © 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim small 2015, 11, No. 35, 4423–4444 www.MaterialsViews.com single particles in microfl uidic environments has become a [ 41–43 ] gold-standard approach in biophysics and cell biology. Yan Jun Liu is currently a research scientist However, it remains a signifi cant challenge to focus light at the Institute of Materials Research and beyond the diffraction limit in order to generate enough Engineering under the Agency for Science, gradient force to trap nanoparticles and biomolecules. As Technology and Research (ASTAR) in Singa- described in the following subsections, SPs offer an excellent pore. He received his PhD in photonics from solution to enhancing the trapping ability of particles and bio- Nanyang Technological University, Singapore, in 2007. His research interests focus on active materials at the nanoscale. Moreover, the photothermal effects plasmonics and metamaterials, liquid crystal associated with the local plasmonic losses provide a unique photonics, and optical sensors. way for low-power and long-range manipulation of fl uids and bubbles. [ 44–59 ] 2.1. Plasmonic Manipulation of Fluids and Bubbles Tony Jun Huang is a professor in the Depart- Enhanced photothermal effects are associated with the non- ment of Engineering Science and Mechanics radiative decay of SPs on metal nanostructures. They arise at The Pennsylvania State University. His re- from the energy relaxation of coherently oscillated electrons search interests are in the fi elds of acoustofl u- upon their interaction with the metal lattice after the exci- idics, optofl uidics, and micro/nano systems for biomedical diagnostics and therapeutics. tation of SPs. [ 60,61 ] In metal nanoparticles,