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Hemmerová E, Homola J. Combining plasmonic and electrochemical biosensing methods. Biosens Bioelectron 2024; 251:116098. [PMID: 38359667 DOI: 10.1016/j.bios.2024.116098] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2023] [Revised: 01/29/2024] [Accepted: 01/31/2024] [Indexed: 02/17/2024]
Abstract
The idea of combining electrochemical (EC) and plasmonic biosensor methods was introduced almost thirty years ago and the potential of electrochemical-plasmonic (EC-P) biosensors has been highlighted ever since. Despite that, the use of EC-P biosensors in analytics has been rather limited so far and the search for unique applications of the EC-P method continues. In this paper, we review the advances in the field of EC-P biosensors and discuss the features and benefits they can provide. In addition, we identify the main challenges for the development of EC-P biosensors and the limitations that prevent EC-P biosensors from more widespread use. Finally, we review applications of EC-P biosensors for the investigation and quantification of biomolecules, and for the study of biomolecular and cellular processes.
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Affiliation(s)
- Erika Hemmerová
- Institute of Photonics and Electronics, Czech Academy of Sciences, Chaberská 1014/57, 182 51, Prague, Czech Republic
| | - Jiří Homola
- Institute of Photonics and Electronics, Czech Academy of Sciences, Chaberská 1014/57, 182 51, Prague, Czech Republic.
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2
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Ma SC, Gupta R, Ondevilla NAP, Barman K, Lee LY, Chang HC, Huang JJ. Voltage-modulated surface plasmon resonance biosensors integrated with gold nanohole arrays. BIOMEDICAL OPTICS EXPRESS 2023; 14:182-193. [PMID: 36698656 PMCID: PMC9842002 DOI: 10.1364/boe.478164] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/21/2022] [Revised: 12/01/2022] [Accepted: 12/01/2022] [Indexed: 06/17/2023]
Abstract
Surface plasmon resonance (SPR) has emerged as one of the most efficient and attractive techniques for optical sensors in biological applications. The traditional approach of an EC (electrochemical)-SPR biosensor to generate SPR is by adopting a prism underneath the sensing substrate, and an angular scan is performed to characterize the reflectivity of target analytes. In this paper, we designed and investigated a novel optical biosensor based on a hybrid plasmonic and electrochemical phenomenon. The SPR was generated from a thin layer of gold nanohole array on a glass substrate. Using C-Reactive Protein (CRP) as the target analyte, we tested our device for different concentrations and observed the optical response under various voltage bias conditions. We observed that SPR response is concentration-dependent and can be modulated by varying DC voltages or AC bias frequencies. For CRP concentrations ranging from 1 to 1000 µg/mL, at the applied voltage of -600 mV, we obtained a limit of detection for this device of 16.5 ng/mL at the resonance peak wavelength of 690 nm. The phenomenon is due to spatial re-distribution of electron concentration at the metal-solution interface. The results suggest that CRP concentration can be determined from the SPR peak wavelength shift by scanning the voltages. The proposed new sensor structure is permissible for various future optoelectronic integration for plasmonic and electrochemical sensing.
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Affiliation(s)
- Syu-Cing Ma
- Graduate Institute of Photonics and Optoelectronics, National Taiwan University, Taipei, Taiwan
- Contributed equally
| | - Rohit Gupta
- Graduate Institute of Photonics and Optoelectronics, National Taiwan University, Taipei, Taiwan
- Contributed equally
| | | | - Kuntal Barman
- Graduate Institute of Photonics and Optoelectronics, National Taiwan University, Taipei, Taiwan
| | - Liang-Yun Lee
- Graduate Institute of Photonics and Optoelectronics, National Taiwan University, Taipei, Taiwan
| | - Hsien-Chang Chang
- Department of Biomedical Engineering, National Cheng Kung University, Tainan, Taiwan
- Medical Device Innovation Center, National Cheng Kung University, Tainan, Taiwan
| | - Jian-Jang Huang
- Graduate Institute of Photonics and Optoelectronics, National Taiwan University, Taipei, Taiwan
- Department of Electrical Engineering, National Taiwan University, Taipei, Taiwan
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3
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Electrochemistry combined-surface plasmon resonance biosensors: A review. Trends Analyt Chem 2022. [DOI: 10.1016/j.trac.2022.116766] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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4
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Terao K, Kondo S. AC-Electroosmosis-Assisted Surface Plasmon Resonance Sensing for Enhancing Protein Signals with a Simple Kretschmann Configuration. SENSORS 2022; 22:s22030854. [PMID: 35161603 PMCID: PMC8838944 DOI: 10.3390/s22030854] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/04/2022] [Revised: 01/19/2022] [Accepted: 01/21/2022] [Indexed: 11/27/2022]
Abstract
A surface plasmon resonance (SPR) sensor chip fabricated with a comb-shaped microelectrode array to supply alternating current (AC) voltage is reported. The chip induces circulating flow near the surface (i.e., AC electroosmosis). The circulating flow provides a mixing effect, which enhances the binding of the analyte molecules. We evaluated the SPR characteristics of the chip and demonstrated an improvement in protein binding to the chip surface. SPR sensor chips with comb-shaped microelectrodes were fabricated using standard UV lithography. Sensing experiments were conducted using a standard Kretschmann-type SPR measurement system. To demonstrate the mixing effect of AC electroosmosis, we evaluated the binding of immunoglobulin G molecules onto the sensor surface where anti-immunoglobulin G antibodies were covalently immobilized. The result indicates that the amount of binding increases by a factor of 1.7 above that achieved by using a conventional chip, suggesting enhancement of the protein signal.
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5
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Komorek P, Jachimska B, Brand I. Adsorption of lysozyme on gold surfaces in the presence of an external electric potential. Bioelectrochemistry 2021; 142:107946. [PMID: 34507162 DOI: 10.1016/j.bioelechem.2021.107946] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2021] [Revised: 07/30/2021] [Accepted: 08/29/2021] [Indexed: 10/20/2022]
Abstract
Adsorbed protein films consist of essential building blocks of many biotechnological and biomedical devices. The electrostatic potential may significantly modulate the protein behaviour on surfaces, affecting their structure and biological activity. In this study, lysozyme was used to investigate the effects of applied electric potentials on adsorption and the protein structure. The pH and the surface charge determine the amount and secondary structure of adsorbed lysozyme on a gold surface. In-situ measurements using polarization modulation infrared reflection absorption spectroscopy indicated that the concentration of both the adsorbed anions and the lysozyme led to conformational changes in the protein film, which was demonstrated by a greater amount of aggregated β-sheets in films fabricated at net positive charges of the Au electrode (Eads > Epzc). The changes in secondary structure involved two parallel processes. One comprised changes in the hydration/hydrogen-bond network at helices, leading to diverse helical structures: α-, 310- and/or π-helices. In the second process β-turns, β-sheets, and random coils displayed an ability to form aggregated β-sheet structures. The study illuminates the understanding of electrical potential-dependent changes involved in the protein misfolding process.
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Affiliation(s)
- Paulina Komorek
- Jerzy Haber Institute of Catalysis and Surface Chemistry Polish Academy of Sciences, Niezapominajek 8, 30-239 Cracow, Poland
| | - Barbara Jachimska
- Jerzy Haber Institute of Catalysis and Surface Chemistry Polish Academy of Sciences, Niezapominajek 8, 30-239 Cracow, Poland.
| | - Izabella Brand
- Department of Chemistry, University of Oldenburg, 26111 Oldenburg, Germany.
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6
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Polonschii C, Gheorghiu M, David S, Gáspár S, Melinte S, Majeed H, Kandel ME, Popescu G, Gheorghiu E. High-resolution impedance mapping using electrically activated quantitative phase imaging. LIGHT, SCIENCE & APPLICATIONS 2021; 10:20. [PMID: 33479199 PMCID: PMC7820407 DOI: 10.1038/s41377-020-00461-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/14/2020] [Revised: 12/16/2020] [Accepted: 12/29/2020] [Indexed: 05/23/2023]
Abstract
Retrieving electrical impedance maps at the nanoscale rapidly via nondestructive inspection with a high signal-to-noise ratio is an unmet need, likely to impact various applications from biomedicine to energy conversion. In this study, we develop a multimodal functional imaging instrument that is characterized by the dual capability of impedance mapping and phase quantitation, high spatial resolution, and low temporal noise. To achieve this, we advance a quantitative phase imaging system, referred to as epi-magnified image spatial spectrum microscopy combined with electrical actuation, to provide complementary maps of the optical path and electrical impedance. We demonstrate our system with high-resolution maps of optical path differences and electrical impedance variations that can distinguish nanosized, semi-transparent, structured coatings involving two materials with relatively similar electrical properties. We map heterogeneous interfaces corresponding to an indium tin oxide layer exposed by holes with diameters as small as ~550 nm in a titanium (dioxide) over-layer deposited on a glass support. We show that electrical modulation during the phase imaging of a macro-electrode is decisive for retrieving electrical impedance distributions with submicron spatial resolution and beyond the limitations of electrode-based technologies (surface or scanning technologies). The findings, which are substantiated by a theoretical model that fits the experimental data very well enable achieving electro-optical maps with high spatial and temporal resolutions. The virtues and limitations of the novel optoelectrochemical method that provides grounds for a wider range of electrically modulated optical methods for measuring the electric field locally are critically discussed.
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Affiliation(s)
| | | | - Sorin David
- International Centre of Biodynamics, 060101, Bucharest, Romania
| | | | - Sorin Melinte
- Institute of Information and Communication Technologies, Electronics and Applied Mathematics, Université Catholique de Louvain, 1348, Louvain-la-Neuve, Belgium
| | - Hassaan Majeed
- Quantitative Light Imaging Laboratory, Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
| | - Mikhail E Kandel
- Quantitative Light Imaging Laboratory, Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
| | - Gabriel Popescu
- Quantitative Light Imaging Laboratory, Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA.
| | - Eugen Gheorghiu
- International Centre of Biodynamics, 060101, Bucharest, Romania.
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7
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Okazaki T, Orii T, Tan SY, Watanabe T, Taguchi A, Rahman FA, Kuramitz H. Electrochemical Long Period Fiber Grating Sensing for Electroactive Species. Anal Chem 2020; 92:9714-9721. [PMID: 32551577 DOI: 10.1021/acs.analchem.0c01062] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We present an electrochemical long period fiber grating (LPFG) sensor for electroactive species with an optically transparent electrode. The sensor was fabricated by coating indium tin oxide onto the surface of LPFG using a polygonal barrel-sputtering method. LPFG was produced by an electric arc-induced technique. The sensing is based on change in the detection of electron density on the electrode surface during potential application and its reduction by electrochemical redox of analytes. Four typical electroactive species of methylene blue, hexaammineruthenium(III), ferrocyanide, and ferrocenedimethanol were used to investigate the sensor performance. The concentrations of analytes were determined by the modulation of the potential as the change in transmittance around the resonance band of LPFG. The sensitivity of the sensor, particularly to methylene blue, was high, and the sensor responded to a wide concentration range of 0.001 mM to 1 mM.
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Affiliation(s)
- Takuya Okazaki
- Department of Environmental Biology and Chemistry, Graduate School of Science and Engineering for Research, University of Toyama, 3190 Gofuku, Toyama 930-8555, Japan.,Department of Applied Chemistry, School of Science and Technology, Meiji University, 1-1-1, Higashimita, Tama-ku, Kawasaki, Kanagawa 214-8571, Japan
| | - Tatsuya Orii
- Department of Environmental Biology and Chemistry, Graduate School of Science and Engineering for Research, University of Toyama, 3190 Gofuku, Toyama 930-8555, Japan
| | - Shin-Yinn Tan
- Faculty of Engineering and Green Technology, Universiti Tunku Abdul Rahman, Jalan Universiti, Bandar Barat, 39100 Kampar, Malaysia
| | - Tomoaki Watanabe
- Department of Applied Chemistry, School of Science and Technology, Meiji University, 1-1-1, Higashimita, Tama-ku, Kawasaki, Kanagawa 214-8571, Japan
| | - Akira Taguchi
- Hydrogen Isotope Research Center, University of Toyama, 3190 Gofuku, Toyama 930-8555, Japan
| | - Faidz A Rahman
- Lee Kong Chian Faculty of Engineering and Science, Universiti Tunku Abdul Rahman, Sungai Long, 43000 Selangor, Malaysia
| | - Hideki Kuramitz
- Department of Environmental Biology and Chemistry, Graduate School of Science and Engineering for Research, University of Toyama, 3190 Gofuku, Toyama 930-8555, Japan
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8
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Costella M, Avenas Q, Frénéa-Robin M, Marchalot J, Bevilacqua P, Charette PG, Canva M. Dielectrophoretic cell trapping for improved surface plasmon resonance imaging sensing. Electrophoresis 2019; 40:1417-1425. [PMID: 30830963 DOI: 10.1002/elps.201800439] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2018] [Revised: 02/21/2019] [Accepted: 02/21/2019] [Indexed: 12/31/2022]
Abstract
The performance of conventional surface plasmon resonance (SPR) biosensors can be limited by the diffusion of the target analyte to the sensor surface. This work presents an SPR biosensor that incorporates an active mass-transport mechanism based on dielectrophoresis and electroosmotic flow to enhance analyte transport to the sensor surface and reduce the time required for detection. Both these phenomena rely on the generation of AC electric fields that can be tailored by shaping the electrodes that also serve as the SPR sensing areas. Numerical simulations of electric field distribution and microparticle trajectories were performed to choose an optimal electrode design. The proposed design improves on previous work combining SPR with DEP by using face-to-face electrodes, rather than a planar interdigitated design. Two different top-bottom electrode designs were experimentally tested to concentrate firstly latex beads and secondly biological cells onto the SPR sensing area. SPR measurements were then performed by varying the target concentrations. The electrohydrodynamic flow enabled efficient concentration of small objects (3 μm beads, yeasts) onto the SPR sensing area, which resulted in an order of magnitude increased SPR response. Negative dielectrophoresis was also used to concentrate HEK293 cells onto the metal electrodes surrounded by insulating areas, where the SPR response was improved by one order of magnitude.
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Affiliation(s)
- Marion Costella
- Université de Lyon, École Centrale de Lyon, Université Claude Bernard Lyon 1, INSA Lyon, CNRS, Ampère, Écully, France.,Laboratoire Nanotechnologies Nanosystèmes (LN2) - CNRS UMI-3463, Université de Sherbrooke, École Centrale de Lyon, Sherbrooke, Canada
| | - Quentin Avenas
- Université de Lyon, École Centrale de Lyon, Université Claude Bernard Lyon 1, INSA Lyon, CNRS, Ampère, Écully, France.,Laboratoire Nanotechnologies Nanosystèmes (LN2) - CNRS UMI-3463, Université de Sherbrooke, École Centrale de Lyon, Sherbrooke, Canada
| | - Marie Frénéa-Robin
- Université de Lyon, École Centrale de Lyon, Université Claude Bernard Lyon 1, INSA Lyon, CNRS, Ampère, Écully, France
| | - Julien Marchalot
- Université de Lyon, École Centrale de Lyon, Université Claude Bernard Lyon 1, INSA Lyon, CNRS, Ampère, Écully, France
| | - Pascal Bevilacqua
- Université de Lyon, École Centrale de Lyon, Université Claude Bernard Lyon 1, INSA Lyon, CNRS, Ampère, Écully, France
| | - Paul G Charette
- Laboratoire Nanotechnologies Nanosystèmes (LN2) - CNRS UMI-3463, Université de Sherbrooke, École Centrale de Lyon, Sherbrooke, Canada.,Institut Interdisciplinaire d'Innovation Technologique (3IT) - Université de Sherbrooke- Sherbrooke, Canada
| | - Michael Canva
- Laboratoire Nanotechnologies Nanosystèmes (LN2) - CNRS UMI-3463, Université de Sherbrooke, École Centrale de Lyon, Sherbrooke, Canada.,Institut Interdisciplinaire d'Innovation Technologique (3IT) - Université de Sherbrooke- Sherbrooke, Canada
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9
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Avenas Q, Moreau J, Costella M, Maalaoui A, Souifi A, Charette P, Marchalot J, Frénéa-Robin M, Canva M. Performance improvement of plasmonic sensors using a combination of AC electrokinetic effects for (bio)target capture. Electrophoresis 2019; 40:1426-1435. [PMID: 30786069 DOI: 10.1002/elps.201800436] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2018] [Revised: 01/15/2019] [Accepted: 02/04/2019] [Indexed: 11/11/2022]
Abstract
Analytes concentration techniques are being developed with the appealing expectation to boost the performance of biosensors. One promising method lies in the use of electrokinetic forces. We present hereafter a new design for a microstructured plasmonic sensor which is obtained by conventional microfabrication techniques, and which can easily be adapted on a classical surface plasmon resonance imaging (SPRI) system without further significant modification. Dielectrophoretic trapping and electro-osmotic displacement of the targets in the scanned fluid are performed through interdigitated 200 μm wide gold electrodes that also act as the SPR-sensing substrate. We demonstrate the efficiency of our device's collection capabilities for objects of different sizes (200 nm and 1 μm PS beads, as well as 5-10 μm yeast cells). SPRI is relevant for the spatial analysis of the mass accumulation at the electrode surface. We demonstrate that our device overcomes the diffusion limit encountered in classical SPR sensors thanks to rapid collection capabilities (<1 min) and we show a consequent improvement of the detection limit, by a factor >300. This study of an original device combining SPRI and electrokinetic forces paves the way to the development of fully integrated active plasmonic sensors with direct applications in life sciences, electrochemistry, environmental monitoring and agri-food industry.
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Affiliation(s)
- Quentin Avenas
- Laboratoire Nanotechnologies et Nanosystèmes, LN2, CNRS - Université de Sherbrooke - INSA Lyon, Sherbrooke, Canada.,Institut des Nanotechnologies de Lyon, CNRS - INSA Lyon - Université Claude Bernard Lyon 1, Villeurbanne, France
| | - Julien Moreau
- Laboratoire Charles Fabry, CNRS - Institut d'Optique Graduate School, Université Paris Saclay, Palaiseau, France
| | - Marion Costella
- Laboratoire Nanotechnologies et Nanosystèmes, LN2, CNRS - Université de Sherbrooke - INSA Lyon, Sherbrooke, Canada.,AMPERE, CNRS - Université de Lyon - École Centrale Lyon - INSA Lyon - Université Claude Bernard Lyon 1 , Ecully, France
| | - Arbi Maalaoui
- Laboratoire Nanotechnologies et Nanosystèmes, LN2, CNRS - Université de Sherbrooke - INSA Lyon, Sherbrooke, Canada.,AMPERE, CNRS - Université de Lyon - École Centrale Lyon - INSA Lyon - Université Claude Bernard Lyon 1 , Ecully, France
| | - Abdelkader Souifi
- Institut des Nanotechnologies de Lyon, CNRS - INSA Lyon - Université Claude Bernard Lyon 1, Villeurbanne, France
| | - Paul Charette
- Laboratoire Nanotechnologies et Nanosystèmes, LN2, CNRS - Université de Sherbrooke - INSA Lyon, Sherbrooke, Canada
| | - Julien Marchalot
- AMPERE, CNRS - Université de Lyon - École Centrale Lyon - INSA Lyon - Université Claude Bernard Lyon 1 , Ecully, France
| | - Marie Frénéa-Robin
- AMPERE, CNRS - Université de Lyon - École Centrale Lyon - INSA Lyon - Université Claude Bernard Lyon 1 , Ecully, France
| | - Michael Canva
- Laboratoire Nanotechnologies et Nanosystèmes, LN2, CNRS - Université de Sherbrooke - INSA Lyon, Sherbrooke, Canada.,Laboratoire Charles Fabry, CNRS - Institut d'Optique Graduate School, Université Paris Saclay, Palaiseau, France
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10
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Šípová-Jungová H, Jurgová L, Mrkvová K, Lynn NS, Špačková B, Homola J. Biomolecular charges influence the response of surface plasmon resonance biosensors through electronic and ionic mechanisms. Biosens Bioelectron 2019; 126:365-372. [DOI: 10.1016/j.bios.2018.11.002] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2018] [Revised: 09/19/2018] [Accepted: 11/01/2018] [Indexed: 12/11/2022]
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11
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Luo X, Deng S, Wang P. Temporal-spatial-resolved mapping of the electrical double layer changes by surface plasmon resonance imaging. RSC Adv 2018; 8:28266-28274. [PMID: 35542477 PMCID: PMC9084293 DOI: 10.1039/c8ra05380d] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2018] [Accepted: 07/30/2018] [Indexed: 11/21/2022] Open
Abstract
An electrical double layer (EDL) is a specific distribution of ions at the electrolyte/electrode interface. As EDL plays a decisive role in the interfacial physical and chemical characteristics, a comprehensive and quantitative understanding of the EDL structure and its change dynamics is important for a wide range of fields, ranging from electrochemistry, energy storage and semiconductor materials to biotechnology. In this paper, we proposed a proof of concept method for temporal- and spatial-resolved mapping of the EDL structure and its change dynamics. A potential was applied on the interface and the potential induced ion re-arrangement process was monitored by surface plasmon resonance (SPR) imaging in real time. NaCl experiments were repeated six times and the coefficient of variation of the results was 5.17%, confirming the potential-induced SPR response. Experiments with different potential excitations, ion concentrations and species were performed and results indicated that the electron density change and ion re-arrangement contributed comparably to the potential induced SPR response. Additionally, the lateral distribution of the EDL formed at the interface between NaCl solutions and an Au film coated with arrays of 11-MUA spots was mapped. This method is temporally and spatially resolved, and thus has the potential to be a promising tool for EDL studies at heterogeneous interfaces.
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Affiliation(s)
- Xueyi Luo
- State Key Laboratory of Precision Measurement Technology and Instruments, Department of Precision Instrument, Tsinghua University Beijing 100084 PR China
| | - Shijie Deng
- State Key Laboratory of Precision Measurement Technology and Instruments, Department of Precision Instrument, Tsinghua University Beijing 100084 PR China
| | - Peng Wang
- State Key Laboratory of Precision Measurement Technology and Instruments, Department of Precision Instrument, Tsinghua University Beijing 100084 PR China
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12
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Kolomenskii AA, Surovic E, Schuessler HA. Optical detection of acoustic waves with surface plasmons. APPLIED OPTICS 2018; 57:5604-5613. [PMID: 30118071 DOI: 10.1364/ao.57.005604] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/10/2018] [Accepted: 06/05/2018] [Indexed: 06/08/2023]
Abstract
For broadband and sensitive detection of acoustic waves, the surface plasmon resonance (SPR) can be used, which responds to variations of dielectric properties in close proximity to a metal film supporting surface plasmon waves. When an acoustic wave is incident onto a receiving plate positioned within the penetration depth of the surface plasmons, it creates displacements of the surface of the plate and thus modulates the dielectric properties, affecting the SPR and the reflection of the incident light. Here we study characteristics and determine the optimal configuration of such an acousto-optical transducer with surface plasmons for efficient conversion of an acoustic signal into an optical one. We simulate the properties of this transducer and present estimates showing that it can have a large frequency bandwidth and high sensitivity.
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13
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Abayzeed SA, Smith RJ, Webb KF, Somekh MG, See CW. Sensitive detection of voltage transients using differential intensity surface plasmon resonance system. OPTICS EXPRESS 2017; 25:31552-31567. [PMID: 29245829 DOI: 10.1364/oe.25.031552] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/21/2017] [Accepted: 09/07/2017] [Indexed: 05/20/2023]
Abstract
This paper describes theoretical and experimental study of the fundamentals of using surface plasmon resonance (SPR) for label-free detection of voltage. Plasmonic voltage sensing relies on the capacitive properties of metal-electrolyte interface that are governed by electrostatic interactions between charge carriers in both phases. Externally-applied voltage leads to changes in the free electron density in the surface of the metal, shifting the SPR position. The study shows the effects of the applied voltage on the shape of the SPR curve. It also provides a comparison between the theoretical and experimental response to the applied voltage. The response is presented in a universal term that can be used to assess the voltage sensitivity of different SPR instruments. Finally, it demonstrates the capacity of the SPR system in resolving dynamic voltage signals; a detection limit of 10mV with a temporal resolution of 5ms is achievable. These findings pave the way for the use of SPR systems in the detection of electrical activity of biological cells.
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14
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Di Martino G, Turek VA, Tserkezis C, Lombardi A, Kuhn A, Baumberg JJ. Plasmonic response and SERS modulation in electrochemical applied potentials. Faraday Discuss 2017; 205:537-545. [PMID: 28879365 DOI: 10.1039/c7fd00130d] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We study the optical response of individual nm-wide plasmonic nanocavities using a nanoparticle-on-mirror design utilised as an electrode in an electrochemical cell. In this geometry Au nanoparticles are separated from a bulk Au film by an ultrathin molecular spacer, giving intense and stable Raman amplification of 100 molecules. Modulation of the plasmonic spectra and the SERS response is observed with an applied voltage under a variety of electrolytes. Different scenarios are discussed to untangle the various mechanisms that can be involved in the electronic interaction between NPs and electrode surfaces.
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Affiliation(s)
- G Di Martino
- NanoPhotonics Centre, Cavendish Laboratory, University of Cambridge, CB3 0HE, UK.
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15
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Laurinavichyute VK, Nizamov S, Mirsky VM. The Role of Anion Adsorption in the Effect of Electrode Potential on Surface Plasmon Resonance Response. Chemphyschem 2017; 18:1552-1560. [PMID: 28294502 DOI: 10.1002/cphc.201601288] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2016] [Indexed: 11/06/2022]
Abstract
Surface plasmon resonance, being widely used in bioanalytics and biotechnology, is influenced by the electrical potential of the resonant gold layer. To evaluate the mechanism of this effect, we have studied it in solutions of various inorganic electrolytes. The magnitude of the effect decreases according to the series: KBr>KCl>KF>NaClO4 . The data were treated by using different models of the interface. A quantitative description was obtained for the model, which takes into account the local dielectric function of gold being affected by the free electron charge, diffuse ionic layer near the gold/water interface, and specific adsorption of halides to the gold surface with partial charge transfer. Taking into account that most biological experiments are performed in chloride-containing solutions, detailed analysis of the model at these conditions was performed. The results indicate that the chloride adsorption is the main mechanism for the influence of potential on the surface plasmon resonance. The dependencies of surface concentration and residual charge of chloride on the applied potential were determined.
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Affiliation(s)
| | - Shavkat Nizamov
- Institute of Biotechnology, Department of Nanobiotechnology, Brandenburg University of Technology Cottbus-Senftenberg, 01968, Senftenberg, Germany
| | - Vladimir M Mirsky
- Institute of Biotechnology, Department of Nanobiotechnology, Brandenburg University of Technology Cottbus-Senftenberg, 01968, Senftenberg, Germany
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16
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Koenderink AF. Single-Photon Nanoantennas. ACS PHOTONICS 2017; 4:710-722. [PMID: 29354664 PMCID: PMC5770162 DOI: 10.1021/acsphotonics.7b00061] [Citation(s) in RCA: 89] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/20/2017] [Revised: 03/07/2017] [Accepted: 03/10/2017] [Indexed: 05/22/2023]
Abstract
Single-photon nanoantennas are broadband strongly scattering nanostructures placed in the near field of a single quantum emitter, with the goal to enhance the coupling between the emitter and far-field radiation channels. Recently, great strides have been made in the use of nanoantennas to realize fluorescence brightness enhancements, and Purcell enhancements, of several orders of magnitude. This perspective reviews the key figures of merit by which single-photon nanoantenna performance is quantified and the recent advances in measuring these metrics unambiguously. Next, this perspective discusses what the state of the art is in terms of fluoresent brightness enhancements, Purcell factors, and directivity control on the level of single photons. Finally, I discuss future challenges for single-photon nanoantennas.
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17
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Wang JG, Fossey JS, Li M, Li DW, Ma W, Ying YL, Qian RC, Cao C, Long YT. Real-time plasmonic monitoring of electrocatalysis on single nanorods. J Electroanal Chem (Lausanne) 2016. [DOI: 10.1016/j.jelechem.2016.10.008] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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18
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Liu W, Niu Y, Viana AS, Correia JP, Jin G. Potential Modulation on Total Internal Reflection Ellipsometry. Anal Chem 2016; 88:3211-7. [PMID: 26889871 DOI: 10.1021/acs.analchem.5b04587] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Electrochemical-total internal reflection ellipsometry (EC-TIRE) has been proposed as a technique to observe the redox reactions on the electrode surface due to its high phase sensitivity to the electrolyte/electrode interface. In this paper, we mainly focus on the influence of the potential modulation on the TIRE response. The analysis suggests that both dielectric constant variation of gold and the electric double layer transformation would modulate the reflection polarization of the surface. For a nonfaradaic process, the signal of TIRE would be proportional to the potential modulation. To testify the analysis, linear sweep voltammetry and open circuit measurement have been performed. The results strongly support the system analysis.
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Affiliation(s)
- Wei Liu
- NML, Institute of Mechanics, Chinese Academy of Sciences , 15 Bei-si-huan West Road, Beijing, 100190, China.,Beijing Key Laboratory of Engineered Construction and Mechanobiology, Institute of Mechanics, Chinese Academy of Sciences , 15 Bei-si-huan West Road, Beijing 100190, China.,University of Chinese Academy of Sciences , 19 Yu-quan Road, Beijing, 100049, China
| | - Yu Niu
- NML, Institute of Mechanics, Chinese Academy of Sciences , 15 Bei-si-huan West Road, Beijing, 100190, China.,Beijing Key Laboratory of Engineered Construction and Mechanobiology, Institute of Mechanics, Chinese Academy of Sciences , 15 Bei-si-huan West Road, Beijing 100190, China
| | - A S Viana
- Centro de Química e Bioquímica, Departamento de Química e Bioquímica, Faculdade de Ciências da Universidade de Lisboa , Ed. C8, Campo Grande, 1749-016 Lisboa, Portugal
| | - Jorge P Correia
- Centro de Química e Bioquímica, Departamento de Química e Bioquímica, Faculdade de Ciências da Universidade de Lisboa , Ed. C8, Campo Grande, 1749-016 Lisboa, Portugal
| | - Gang Jin
- NML, Institute of Mechanics, Chinese Academy of Sciences , 15 Bei-si-huan West Road, Beijing, 100190, China.,Beijing Key Laboratory of Engineered Construction and Mechanobiology, Institute of Mechanics, Chinese Academy of Sciences , 15 Bei-si-huan West Road, Beijing 100190, China
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19
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Wu C, Rehman FU, Li J, Ye J, Zhang Y, Su M, Jiang H, Wang X. Real-Time Evaluation of Live Cancer Cells by an in Situ Surface Plasmon Resonance and Electrochemical Study. ACS APPLIED MATERIALS & INTERFACES 2015; 7:24848-24854. [PMID: 26492438 DOI: 10.1021/acsami.5b08066] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
This work presents a new strategy of the combination of surface plasmon resonance (SPR) and electrochemical study for real-time evaluation of live cancer cells treated with daunorubicin (DNR) at the interface of the SPR chip and living cancer cells. The observations demonstrate that the SPR signal changes could be closely related to the morphology and mass changes of adsorbed cancer cells and the variation of the refractive index of the medium solution. The results of light microscopy images and 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide studies also illustrate the release or desorption of HepG2 cancer cells, which were due to their apoptosis after treatment with DNR. It is evident that the extracellular concentration of DNR residue can be readily determined through electrochemical measurements. The decreases in the magnitudes of SPR signals were linearly related to cell survival rates, and the combination of SPR with electrochemical study could be utilized to evaluate the potential therapeutic efficiency of bioactive agents to cells. Thus, this label-free, real-time SPR-electrochemical detection technique has great promise in bioanalysis or monitoring of relevant treatment processes in clinical applications.
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Affiliation(s)
- Changyu Wu
- State Key Laboratory of Bioelectronics (Chien-Shiung Wu Laboratory), Southeast University , Nanjing 210096, China
| | - Fawad Ur Rehman
- State Key Laboratory of Bioelectronics (Chien-Shiung Wu Laboratory), Southeast University , Nanjing 210096, China
| | - Jingyuan Li
- Laboratory Animal Center, Nantong University , Nantong 226001, China
| | - Jing Ye
- State Key Laboratory of Bioelectronics (Chien-Shiung Wu Laboratory), Southeast University , Nanjing 210096, China
| | - Yuanyuan Zhang
- State Key Laboratory of Bioelectronics (Chien-Shiung Wu Laboratory), Southeast University , Nanjing 210096, China
| | - Meina Su
- State Key Laboratory of Bioelectronics (Chien-Shiung Wu Laboratory), Southeast University , Nanjing 210096, China
| | - Hui Jiang
- State Key Laboratory of Bioelectronics (Chien-Shiung Wu Laboratory), Southeast University , Nanjing 210096, China
| | - Xuemei Wang
- State Key Laboratory of Bioelectronics (Chien-Shiung Wu Laboratory), Southeast University , Nanjing 210096, China
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20
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Liquid-Crystal-Enabled Active Plasmonics: A Review. MATERIALS 2014; 7:1296-1317. [PMID: 28788515 PMCID: PMC5453087 DOI: 10.3390/ma7021296] [Citation(s) in RCA: 136] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/17/2014] [Revised: 02/01/2014] [Accepted: 02/12/2014] [Indexed: 01/20/2023]
Abstract
Liquid crystals are a promising candidate for development of active plasmonics due to their large birefringence, low driving threshold, and versatile driving methods. We review recent progress on the interdisciplinary research field of liquid crystal based plasmonics. The research scope of this field is to build the next generation of reconfigurable plasmonic devices by combining liquid crystals with plasmonic nanostructures. Various active plasmonic devices, such as switches, modulators, color filters, absorbers, have been demonstrated. This review is structured to cover active plasmonic devices from two aspects: functionalities and driven methods. We hope this review would provide basic knowledge for a new researcher to get familiar with the field, and serve as a reference for experienced researchers to keep up the current research trends.
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21
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Zhang LL, Chen X, Wei HT, Li H, Sun JH, Cai HY, Chen JL, Cui DF. An electrochemical surface plasmon resonance imaging system targeting cell analysis. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2013; 84:085005. [PMID: 24007100 DOI: 10.1063/1.4819027] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
This paper presents an electrochemical-surface plasmon resonance imaging (EC-SPRI) system, enabling the characterization of optical and electrical properties of cells, simultaneously. The developed surface plasmon resonance (SPR) imaging system was capable of imaging micro cavities with a dimension of 10 μm × 10 μm and differentiated glycerol solutions with a group of refractive indices (RIs). Furthermore, the EC-SPRI system was used to image A549 cells, suggesting corresponding RI and morphology changes during the cell death process. In the end, electrochemical and SPR methods were used in combination, recording oxidation peaks of A549 cells in the cyclic voltage curves and SPR response unit increase, simultaneously.
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Affiliation(s)
- L L Zhang
- State Key Laboratory of Transducer Technology, Institute of Electronics, Chinese Academy of Sciences, Beijing, China
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22
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Facile fabrication of an interface for online coupling of microchip CE to surface plasmon resonance. Bioanalysis 2012; 4:373-9. [DOI: 10.4155/bio.12.4] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Background: The aim was to develop a simple route to coupling microchip CE (MCE) to surface plasmon resonance (SPR). MCE is a microfluidic technology that utilizes microfabrication techniques to connect interacting fluid reservoirs. Its advantages include rapid analysis (typically seconds), easy integration of multiple analytical steps and parallel operation. SPR detects changes in refractive index within a short distance from the surface of a thin metal film as variations in light intensity reflected from the back of the film and, thus, does not require labeling. There is a great demand for developing hyphenated techniques like MCE–SPR that are fast, sensitive and inexpensive to analyze biological materials. Materials & Methods: The separation channel and flow cell exist as overlapping regions constructed during the microchip production and buffer solution was delivered mechanically. Such a design has successfully isolated the electrical field inherent in the MCE from the SPR detector. Consequently, the potential interference to the SPR signal (or modulation of the density of surface plasmons at the gold chip) is circumvented. Results: The limits of detection for bovine serum albumin and sodium fluorescein were determined to be 7.5 µM and 3.1 mM, respectively. Conclusion: The technique described, herein, has been successfully applied in the separation of two species. The method offers the advantages of a near zero connection dead volume, electrical shielding from the separation voltage and minimization of the mass transfer effect.
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23
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Bolduc OR, Correia-Ledo D, Masson JF. Electroformation of peptide self-assembled monolayers on gold. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2012; 28:22-26. [PMID: 22149095 DOI: 10.1021/la203493v] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
The application of a potential to deposit a monolayer of 3-mercaptopropionic acid-histidinyl-histidinyl-histidinyl-aspartyl-aspartyl (3-MPA-HHHDD-OH) controls the density and molecular structure of the peptide monolayer, which results in different wettabilities of the surface, surface density, orientation of the molecule (extended or bent), and nonspecific adsorption of serum proteins. 3-MPA-HHHDD-OH must be deposited at 200 mV to maintain an extended configuration, which promoted low biofouling properties.
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Affiliation(s)
- Olivier R Bolduc
- Département de Chimie, Université de Montréal, C. P. 6128 Succ. Centre-Ville, Montréal, QC, Canada H3C 3J7
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24
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Gupta G, Bhaskar A, Tripathi B, Pandey P, Boopathi M, Rao PL, Singh B, Vijayaraghavan R. Supersensitive detection of T-2 toxin by the in situ synthesized π-conjugated molecularly imprinted nanopatterns. An in situ investigation by surface plasmon resonance combined with electrochemistry. Biosens Bioelectron 2011; 26:2534-40. [DOI: 10.1016/j.bios.2010.10.050] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2010] [Revised: 10/12/2010] [Accepted: 10/28/2010] [Indexed: 12/01/2022]
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25
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Zhang J, Atay T, Nurmikko AV. Optical detection of brain cell activity using plasmonic gold nanoparticles. NANO LETTERS 2009; 9:519-24. [PMID: 19199762 DOI: 10.1021/nl801891q] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Metal nanoparticles are being actively explored for applications that use localized surface plasmon (LSP) resonance for optical sensing. Here we report an electrostatic field sensing technique which has been applied to detection of mammalian brain cell activity, by optically measuring the cellular potential induced shift in the SP resonance mode of an adjacent planar gold nanoparticle array. An experimental scheme was first devised which enables a quantitative calibration of the field-induced plasmon resonance modulation in air. Hippocampal (brain) neural cells were then grown onto the nanoparticle template and cellular level individual transient signals were detected optically when the chemically triggered neurons switched their potential. Experimental data are compared with calculations using the Drude model for the dielectric response of gold and the Stern model for the metal-electrolyte junction, with good agreement.
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Affiliation(s)
- Jiayi Zhang
- Department of Physics, Brown University, Providence, Rhode Island 02912, USA
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26
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Sanabria H, Miller JH, Mershin A, Luduena RF, Kolomenski AA, Schuessler HA, Nanopoulos DV. Impedance spectroscopy of alpha-beta tubulin heterodimer suspensions. Biophys J 2006; 90:4644-50. [PMID: 16732057 PMCID: PMC1471852 DOI: 10.1529/biophysj.106.069427] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Impedance spectroscopy is a technique that reveals information, such as macromolecular charges and related properties about protein suspensions and other materials. Here we report on impedance measurements over the frequency range of 1 Hz to 1 MHz of alpha-beta tubulin heterodimers suspended in a buffer. These and other polyelectrolyte suspensions show enormous dielectric responses at low frequencies, due both to the motion of charges suspended in the medium and to an electrical double layer that forms at each electrode-medium interface. We propose an equivalent circuit model to minimize electrode polarization effects and extract the intrinsic response of the bulk medium. At megaHertz frequencies, the conductivity increases with concentration below the critical concentration of approximately 1 mg/ml for microtubule polymerization, above which the conductivity decreases. This suggests that such measurements can be used to monitor the dynamics of microtubule polymerization. Finally, we obtain the net charge number per tubulin dimer of /Z/ = 306 in the saline buffer, which, if maintained as the dimers polymerized, would yield a linear charge density of 3.8 e/angstroms for the assembled microtubules. These results are potentially important for fundamental electrostatic processes in biomolecules and suggest the possibility of developing future bioelectronic applications.
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Affiliation(s)
- Hugo Sanabria
- Department of Physics and Texas Center for Superconductivity at University of Houston, Houston, Texas 77204, USA
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27
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Yang X, Wang Q, Wang K, Tan W, Yao J, Li H. Electrical switching of DNA monolayers investigated by surface plasmon resonance. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2006; 22:5654-9. [PMID: 16768490 DOI: 10.1021/la052907m] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
The switching of DNA monolayers between a "lying" and a "standing" state initiated by applying electric field, and the subsequent DNA hybridization at different states were investigated in a contactless, label-free mode by surface plasmon resonance (SPR) technique. The results showed that the strength of the electric field and surface coverage could influence the switching of DNA monolayers. In addition, it was found that DNA hybridization efficiency could be enhanced or decreased when DNA probes stood straight up or lay flat on the gold surface, depending on the potential of the gold substrate. The enhancement of DNA hybridization efficiency reached the maximum when surface coverage reached 5.87 x 10(12) molecules/cm(2) and the potential of gold substrate was more negative than -0.7 V (versus ITO-coated glass). The research may be helpful for the construction of sensitive biosensors, biochips, and nanoscale electronic devices.
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Affiliation(s)
- Xiaohai Yang
- State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, Hunan University, Bio-Nano Technology Engineering Research Center of Hunan Province, Changsha, People's Republic of China
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28
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Mershin A, Kolomenski AA, Schuessler HA, Nanopoulos DV. Tubulin dipole moment, dielectric constant and quantum behavior: computer simulations, experimental results and suggestions. Biosystems 2005; 77:73-85. [PMID: 15527947 DOI: 10.1016/j.biosystems.2004.04.003] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2004] [Revised: 04/23/2004] [Accepted: 04/26/2004] [Indexed: 10/26/2022]
Abstract
We used computer simulation to calculate the electric dipole moments of the alpha- and beta-tubulin monomers and dimer and found those to be |p(alpha)| = 552D, |p(beta)| = 1193D and |p(alphabeta)| = 1740D, respectively. Independent surface plasmon resonance (SPR) and refractometry measurements of the high-frequency dielectric constant and polarizability strongly corroborated our previous SPR-derived results, giving Deltan/Deltac approximately 1.800 x 10(-3)ml/mg. The refractive index of tubulin was measured to be n(tub) approximately 2.90 and the high-frequency tubulin dielectric constant k(tub) approximately 8.41, while the high-frequency polarizability was found to be alpha(tub) approximately 2.1 x 10(-33)C m(2)/V. Methods for the experimental determination of the low-frequency p are explored, as well as ways to test the often conjectured quantum coherence and entanglement properties of tubulin. Biobits, bioqubits and other applications to bioelectronics are discussed.
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Affiliation(s)
- A Mershin
- Department of Physics, Texas A&M University, College Station, TX 77843-4242, USA.
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