Editorial Cite This: ACS Photonics 2017, 4, 2382-2384
pubs.acs.org/journal/apchd5
Virtual Issue on Plasmonic-Based Sensing Romain Quidant, Associate Editor, ACS Photonics ICFO − The Institute of Photonic Sciences & ICREA - Institució Catalana de recerca i Estudis avançats, Barcelona, Spain
Bin Ren, Associate Editor, Analytical Chemistry Xiamen University, Xiamen, China
Michael J. Sailor, Associate Editor, ACS Sensors University of California, San Diego, San Diego, United States
M
graphene resonator can be tuned through the entire molecular IR absorption spectrum by electrically changing the graphene doping, thus probing the entire SEIRA spectrum. Since the early works on plasmon biosensing, many efforts have been devoted to increasing the sensor response while minimizing any source of experimental uncertainty. One strategy consists in engineering the sensing mode and adapt it optimally to the specific feature of the analyte. In Mazzotta et al.,3 the authors nicely show that, depending on the size of the detected molecule, arrays of gold nanodisks would perform better than arrays of nanoholes. Yet, the sensitivity is foreseen to be limited by the shot noise limit (SNL). Recently, two ACS Photonics articles suggested the use of the quantum optics tool box in order to push the noise floor in plasmonic sensing below the SNL. Particularly, Pooser et al.4 show the use of “two-mode light squeezing” to interrogate a conventional surface plasmon resonance (SPR) sensor formed by an extended metal film, thus, enabling faster detection or reaching lower detection levels. Using theoretical modeling, Lee et al.5 recently extended a similar concept to a more sophisticated plasmonic sensing scheme based on plasmonic interferometry with different kinds of metal waveguides. Pushing the sensitivity of plasmonic sensing can also be addressed by using an alternative transduction mechanism that would be more sensitive to the presence of molecules at the sensor surface. Along this line, Caballero et al.6 propose using an Au−Co−Au film perforated with a periodic array of nanoholes as a new magneto-optical surface plasmon sensor. By detecting the transverse magneto-optical Kerr effect, they predict theoretically a 2 orders of magnitude improvement in sensitivity. Another emerging trend in plasmonic-based sensing is related to extending the amount of information extracted from the analyte. In particular, there is a growing interest in exploiting plasmonics to assess a biomolecule’s chirality, a key molecular feature especially important to the pharmaceutical industry. To this aim, the articles by Nesterov et al.7 and Poulikakos et al.8 investigate fundamental aspects of plasmon-
etallic nanoparticles or nanostructures are among the most fascinating nanomaterials because of their unique localized surface plasmon resonances (LSPR). They display very strong interaction with light over a diverse range of wavelengths, and this leads to interesting near field effects, strong scattering signals, and photothermal phenomena. Important applications for metallic nanoparticles (in particular, those comprised of silver and gold) include surface-enhanced spectroscopy (infrared and Raman), single particle tracking, and photothermal imaging and therapy. As the energies of plasmon modes are sensitive to local environment and aggregation state, plasmonic nanoparticles have found widespread use in colorimetric sensing. Current sensor-related research themes in plasmonics have focused on enhancing detection sensitivity, improving reliability, and adding molecular specificity. In this virtual issue, we have selected 29 articles recently published in ACS Photonics, ACS Sensors, and Analytical Chemistry, which highlight some of the latest technological trends in plasmonic-based sensing. The articles from ACS Photonics address the subject of plasmon-enhanced molecular infrared (IR) spectroscopy, either based on noble metals (Huck et al.)1 or graphene (Marini et al.).2 These studies highlight the growing interest in accessing the IR fingerprint of biomolecules for molecular sensing. Similar to Surface-Enhanced Raman Spectroscopy (SERS), low signals observed in IR spectroscopy can be efficiently boosted using the enhanced optical field created by resonant noble metal nanostructures (known as SEIRA, Surface-Enhanced Infrared Absorption). In a recent paper, Huck et al. engineer plasmonic modes of gold nanoantennas in order to maximize this SEIRA enhancement. Their approach consists of suspending the gold nanoantenna on a silicon pedestal in order to reduce the substrate influence and make available the antenna hotspots to the analyte. Interestingly, they also show that further control can be achieved by adjusting the pedestal height. A complementary strategy to metal-based SEIRA, recently proposed by Marini et al., combines the huge field confinement of graphene in the IR with its electric tunability to achieve very accurate IR spectroscopy without needing a spectrometer. In such a configuration, the analyte molecule sits a few nanometers away from a doped graphene disk resonator of a few hundred nanometers in diameter. The resonance of the © 2017 American Chemical Society
Received: September 14, 2017 Accepted: September 18, 2017 Published: October 18, 2017 2382
DOI: 10.1021/acsphotonics.7b01062 ACS Photonics 2017, 4, 2382−2384
ACS Photonics
Editorial
ing. The immunosensors developed in this work were able to monitor, in real time, the specific attachment of intact cells on the order of 3 × 106 cells mL−1 and has the potential to be used as a disposable device for in situ and real-time clinical diagnosis. The articles from ACS Sensors also address the range of issues that limit current sensor technologies−and chief among these are sensitivity and specificity. The exquisite sensitivity that a plasmonic nanostructure shows to its local environment can be manifested in both the wavelength and the intensity of the plasmon band, and Zhang and Xia show that combining both of these spectral features provides greater fidelity and sensitivity in detecting metal ions in water.19 Gkogkou et al.20 show that wavelength interacts strongly with polarization of the incoming light in the response of a plasmonic nanostructure to a given analyte (in the case of SERS detection of small molecule analytes), and that the two parameters of polarization and wavelength can be traded to improve specificity of the sensor. In this latter paper, the high polarization sensitivity is a consequence of the aligned rows of undulated silver nanostructures used in the study. While two-dimensional structures such as these (and one-dimensional dots) are commonly used because of the relative ease with which they can be fabricated, an emerging theme in plasmonic sensors is a rapidly expanding set of tools researchers are developing to build increasingly more elaborate nanostructures. Enabled by new and innovative synthetic methods,21−23 this emphasis on nanostructure design is driven by the desire to build new, unique shapes that show large localized surface plasmon features that will then increase sensitivity or otherwise improve sensor performance. A beautiful example of such “thoughtfully designed” plasmonic nanostructures is the hollow nanostructures described by Hazra and Chandra.24 In this case, the structures are equilateral prismatic gold nanoparticles that contain a spherical interior cavity. Hazra and Chandra show that these materials display RI sensitivity greater than solid nanorods, nanostars and other hollow nanocages. The specificity of any sensor is often limited by interferents in the matrix, and this is a particular challenge for biosensors that must operate in messy and highly varied matrices such as human serum.25 Aube et al.26 and Zhou et al.27 provide solutions to this problem. In the case of Aube et al., it is by augmenting the direct analyte-capture probe interaction with a secondary detection step involving a second capture probe for the analyte (an antibody), reminiscent of the well-known sandwich assay. In the case of Zhou et al., it is by using a somewhat porous “basil-seed” plasmonic nanostructure that allows the expulsion of excess matrix, increasing optical transparency in the region of the assay. Molecular imprinting is an alternative to the more common antibody capture probe that is also readily incorporated onto metallic nanostructures.28 Pellegrotti et al.29 show how a plasmonic system could be used to further enhance specificity of molecular recognition elements, by inducing local heating that can selectively modulate emission from a molecular fluorophore. Plasmonics is certainly a vibrant field and its capability as a sensitive analytical method is yet to be explored. We believe the articles selected in this virtue issue will point out the direction of the field and push plasmon-based sensing for practical analytical applications.
enhanced circular dichroism (CD) that could greatly contribute to improve its efficacy. Nesterov et al. study numerically how plasmonic antennas can be engineered to optimize their optical near field for maximizing CD at the antenna resonance. The work by Poulikakos et al. is complementary since it proposes a novel far field observable, which is more reliable than CD, on the chiral optical near field. SERS is an important field of plasmonics as it can provide the fingerprint information on target species and allow label free detection. In an article published in Analytical Chemistry, Hong et al.9 proposed a new detection scheme by plasmonic trapping of gold nanoparticles in the gap of initially fabricated nanobowtie structures. In this configuration, the hot spot formed by the gold nanoparticles (AuNP) is excited to produce a strong Raman signal. Furthermore, Masson et al.10 developed a plasmonic “patch clamp” nanopipette for SERS detection of biomolecules; the SERS response was obtained from a plasmon coupling between a captured AuNP on a nanotip, a second AuNP modified with a Raman active reporter, and an antibody selective for immunoglobulin G (IgG). Fundamental studies aimed at understanding and optimizing the interaction of light with metal nanostructures is of growing interest in sensing applications, and these have led to new approaches to probe nanostructures and new ways to harness their interesting photophysics. Liu et al.11 proposed an experimental method to simultaneously measure extinction and scattering spectra of plasmonic nanoparticles, which may help guide the synthesis of suitable plasmonic nanoparticles for specific applications such as photothermal spectroscopy. An ultrasensitive background-free photothermal-based technique, differential detection photothermal interferometry (DDPI), has been developed by Maceiczyk et al.12 to quantitatively detect plasmonic nanoparticles at femtomolar concentrations and at linear flow speeds as high as 100 mm/s (400 particles per second). Recently, Liang et al.13 proposed a novel plasmonicbased electrochemical impedance microscopy (P-EIM) technique, which measures electrical impedance optically by converting changes in surface charge to changes in SPR image contrast, to quantitatively study small molecule binding kinetics on protein microarrays. In the emerging field of chiroplasmonics, Liu et al.14 presented an efficient method to form DNA-induced assemblies of AuNPs, which exhibit strong chiroptical activity. Upon interaction of the assembly with a biomarker of the oxidative DNA damage, the CD intensity shows a linear decrease with the increase of the concentration. An alternative strategy to evaluate LSPR responses utilizing changes in the curvature of the extinction spectrum has been developed by Liedberg et al.,15 which they have found to be superior to monitoring peak shifts or changes in extinction, both in terms of signal-to-noise ratio and reliability of the sensor. In the field of plasmonic colorimetric sensing, some exciting new strategies to realize a sensitive response have emerged. For example, Hao et al.16 demonstrated a high-throughput and sensitive colorimetric assay for H2S. The technique uses H2S to etch silver from gold/silver core/shell single plasmonic nanoparticles. Moreover, Poon et al.17 have developed a simple yet robust approach to quantification by binding modified gold and silver nanoparticles to the target species and then quantifying the intensity of light scattered from a single nanoparticle in the dark field image. Finally, Malachovská et al.18 used SPR from gold-coated, tilted fiber Bragg gratings for selective cellular detection through membrane protein target-
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AUTHOR INFORMATION
ORCID
Romain Quidant: 0000-0001-8995-8976 2383
DOI: 10.1021/acsphotonics.7b01062 ACS Photonics 2017, 4, 2382−2384
ACS Photonics
Editorial
(19) Zhang, H.; Xia, Y. Ratiometry, Wavelength, and Intensity: Triple Signal Readout for Colorimetric Sensing of Mercury Ions by Plasmonic Cu2-xSe Nanoparticles. ACS Sens. 2016, 1, 384−391. (20) Gkogkou, D.; Schreiber, B.; Shaykhutdinov, T.; Ly, H. K.; Kuhlmann, U.; Gernert, U.; Facsko, S.; Hildebrandt, P.; Esser, N.; Hinrichs, K.; Weidinger, I. M.; Oates, T. W. H. Polarization- and Wavelength-Dependent Surface-Enhanced Raman Spectroscopy Using Optically Anisotropic Rippled Substrates for Sensing. ACS Sens. 2016, 1, 318−323. (21) Bagheri, S.; Strohfeldt, N.; Sterl, F.; Berrier, A.; Tittl, A.; Giessen, H. Large-Area Low-Cost Plasmonic Perfect Absorber Chemical Sensor Fabricated by Laser Interference Lithography. ACS Sens. 2016, 1, 1148−1154. (22) Braun, A.; Maier, S. A. Versatile Direct Laser Writing Lithography Technique for Surface Enhanced Infrared Spectroscopy Sensors. ACS Sens. 2016, 1, 1155−1162. (23) Jia, P.; Yang, Z.; Yang, J.; Ebendorff-Heidepriem, H. Quasiperiodic Nanohole Arrays on Optical Fibers as Plasmonic Sensors: Fabrication and Sensitivity Determination. ACS Sens. 2016, 1, 1078−1083. (24) Hazra, B.; Chandra, M. Plasmon Hybridization Mediated Structure-Specific Refractive Index Sensitivity of Hollow Gold Nanoprism in the Vis-NIR Region. ACS Sens. 2016, 1, 536−542. (25) Masson, J.-F. Surface Plasmon Resonance Clinical Biosensors for Medical Diagnostics. ACS Sens. 2017, 2, 16−30. (26) Aube, A.; Charbonneau, D. M.; Pelletier, J. N.; Masson, J.-F. Response Monitoring of Acute Lymphoblastic Leukemia Patients Undergoing L-Asparaginase Therapy: Successes and Challenges Associated with Clinical Sample Analysis in Plasmonic Sensing. ACS Sens. 2016, 1, 1358−1365. (27) Zhou, N.; Zhou, Q.; Meng, G.; Huang, Z.; Ke, Y.; Liu, J.; Wu, N. Incorporation of a Basil-Seed-Based Surface Enhanced Raman Scattering Sensor with a Pipet for Detection of Melamine. ACS Sens. 2016, 1, 1193−1197. (28) Guerreiro, J. R. L.; Bochenkov, V. E.; Runager, K.; Aslan, H.; Dong, M.; Enghild, J. J.; De Freitas, V.; Ferreira Sales, M. G.; Sutherland, D. S. Molecular Imprinting of Complex Matrices at Localized Surface Plasmon Resonance Biosensors for Screening of Global Interactions of Polyphenols and Proteins. ACS Sens. 2016, 1, 258−264. (29) Pellegrotti, J. V.; Cortes, E.; Bordenave, M. D.; Caldarola, M.; Kreuzer, M. P.; Sanchez, A. D.; Ojea, I.; Bragas, A. V.; Stefani, F. D. Plasmonic Photothermal Fluorescence Modulation for Homogeneous Biosensing. ACS Sens. 2016, 1, 1351−1357.
Bin Ren: 0000-0002-9821-5864 Michael J. Sailor: 0000-0002-4809-9826 Notes
Views expressed in this editorial are those of the authors and not necessarily the views of the ACS.
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REFERENCES
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DOI: 10.1021/acsphotonics.7b01062 ACS Photonics 2017, 4, 2382−2384
