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Metal nanostructures offer means to control light at the nanoscale via collective charge oscillations called plasmons. This resonant phenomenon is sensitive to changes in the local environment, which others and we have used extensively for biosensing applications. Plasmonic nanostructures can also be used for light-to-heat conversion at the nanoscale, enabled by non-radiative plasmon decay. I will discuss how to use such plasmonic heating in combination with organic materials for sensing applications [1,2] and present our recent research on plasmons also in organic nanostructures [3]. 1 M. Shiran Chaharsoughi, D. Tordera, A. Grimoldi, I. Engquist, M. Berggren, S. Fabiano and M.P. Jonsson, Adv. Opt. Mat. 6, 1 (2018) 2 M.S. Chaharsoughi, D. Zhao, X. Crispin, S. Fabiano and M.P. Jonsson, Adv. Fun. Mat. 29, 1 (2019) 3 S. Chen, E.S.H. Kang, M.S. Chaharsoughi, V. Stanishev, P. Kuhne, H. Sun, C. Wang, M. Fahlman, S. Fabiano, V. Darakchieva and M.P. Jonsson, Nature Nano. 15, 35 (2020)

Plasmonic nanostructures have been explored for a wide variety of applications due to their ability to control light at the nanoscale. However, plasmonic nanoantennas based on conventional metals are difficult to tune after fabrication due to fixed material properties. By contrast, the properties of organic conducting polymers can be tuned via their redox state, and they can be optically metallic in their oxidized state [1]. Here, I will present our recent work demonstrating that nanodisks of a highly conducting polymer can sustain plasmonic resonances in the near-infrared and act as switchable optical nanoantennas [2]. 1 S. Chen, P. Kuhne, V. Stanishev, S. Knight, R. Brooke, I. Petsagkourakis, X. Crispin, M. Schubert, V. Darakchieva, and M.P. Jonsson, J. Mater. Chem. C 7, 4350 (2019). 2 S. Chen, E.S.H. Kang, M.S. Chaharsoughi, V. Stanishev, P. Kuhne, H. Sun, C. Wang, M. Fahlman, S. Fabiano, V. Darakchieva, and M.P. Jonsson, Nature Nanotech. 15, 35 (2020).

Certain bird species have evolved spectacular colors that arise from organized nanostructures of melanin. Its high refractive index (similar to 1.8) and broadband absorptive properties enable vivid structural colors that are nonsusceptible to photo-bleaching. Mimicking natural melanin structural coloration could enable several important applications, in particular, for non-iridescent systems with colors that are independent of incidence angle. Here, we address this by forming melanin photonic crystal microdomes by inkjet printing. Owing to their curved nature, the microdomes exhibit noniridescent vivid structural coloration, tunable throughout the visible range via the size of the nanoparticles. Large-area arrays (>1 cm(2)) of high-quality photonic microdomes could be printed on both rigid and flexible substrates. Combined with scalable fabrication and the nontoxicity of melanin, the presented photonic microdomes with noniridescent structural coloration may find use in a variety of applications, including sensing, displays, and anticounterfeit holograms. Funding Agencies|Wenner-Gren Foundation; Swedish Research CouncilSwedish Research Council; Knut and Alice Wallenberg foundationKnut & Alice Wallenberg Foundation; Swedish Foundation for Strategic researchSwedish Foundation for Strategic Research; Linkoping University; Wallenberg Wood Science Center the Wallenberg Wood Science Centre; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009 00971]

Plasmonic color generation offers several advantages but is also limited by the cost and availability of noble metals like gold. In this work, we present color-tunable metasurfaces with high chromaticity and reflectivity consisting of an aluminum mirror, a dielectric spacer, and a plasmonic nanohole array in copper. Copper is shown to be an excellent alternative to gold when properly protected from oxidation and makes it possible to generate a wide RGB gamut covering 27% of the standard RGB. By patterning the metasurfaces into microscale pixel triplets, color photos can be well reproduced with high resolution over wafer-sized areas. Further, we demonstrate active modulation of the reflected intensity using an electrochromic conductive polymer deposited on top of the nanostructures by screen printing. This technology opens up for ultrathin and flexible reflective displays in full color, that is, plasmonic electronic paper, compatible with large-scale sustainable production. Funding agencies: Swedish Foundation for Strategic Research [RMA11-0037]; Wenner-Gren Foundations; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009 00971]; Chalmers Nanoscience and Nanotechnology Area of

Nonradiative decay of plasmons in metallic nanostructures offers unique means for light-to-heat conversion at the nanoscale. Typical thermoplasmonic systems utilize discrete particles, while metal nanohole arrays were instead considered suitable as heat sinks to reduce heating effects. By contrast, we show for the first time that under uniform broadband illumination (e.g., the sun) ultrathin plasmonic nanohole arrays can be highly competitive plasmonic heaters and provide significantly higher temperatures than analogous nanodisk arrays. Our plasmonic nanohole arrays also heat significantly more than nonstructured metal films, while simultaneously providing superior light transmission. Besides being efficient light-driven heat sources, these thin perforated gold films can simultaneously be used as electrodes. We used this feature to develop "plasmonic thermistors" for electrical monitoring of plasmon-induced temperature changes. The nanohole arrays provided temperature changes up to 7.5 K by simulated sunlight, which is very high compared to previously reported plasmonic systems under similar conditions (solar illumination and ambient conditions). Both temperatures and heating profiles quantitatively agree with combined optical and thermal simulations. Finally, we demonstrate the use of a thermoplasmonic nanohole electrode to power the first hybrid plasmonic ionic thermoelectric device, resulting in strong solar-induced heat gradients and corresponding thermoelectric voltages. Funding Agencies|Wenner-Gren Foundations; Swedish Research Council; Swedish Foundation for Strategic Research; AForsk Foundation; Knut and Alice Wallenberg Foundation; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [SFO-Mat-LiU No 2009 00971]

The coupling between charge accumulation in a conjugated polymer and the ionic charge compensation, provided from an electrolyte, defines the mode of operation in a vast array of different organic electrochemical devices. The most explored mixed organic ion-electron conductor, serving as the active electrode in these devices, is poly(3,4-ethyelenedioxythiophene) doped with polystyrelensulfonate (PEDOT:PSS). In this progress report, scientists of the Laboratory of Organic Electronics at Linkoping University review some of the achievements derived over the last two decades in the field of organic electrochemical devices, in particular including PEDOT:PSS as the active material. The recently established understanding of the volumetric capacitance and the mixed ion-electron charge transport properties of PEDOT are described along with examples of various devices and phenomena utilizing this ion-electron coupling, such as the organic electrochemical transistor, ionic-electronic thermodiffusion, electrochromic devices, surface switches, and more. One of the pioneers in this exciting research field is Prof. Olle Inganas and the authors of this progress report wish to celebrate and acknowledge all the fantastic achievements and inspiration accomplished by Prof. Inganas all since 1981. Funding Agencies|Knut and Alice Wallenberg Foundation; Swedish Research Council; Onnesjo Foundation; Swedish Foundation for Strategic Research; European Commission; Wenner-Gren Foundations; AForsk Foundation; strategic research area of Advanced Functional Materials at Linkoping University; Vinnova

Plasmonic metasurfaces based on ensembles of distributed metallic nanostructures can absorb, scatter, and in other ways shape light at the nanoscale. Forming hybrid plasmonic metasurfaces by combination with other materials opens up for new research directions and novel applications. This perspective highlights some of the recent advancements in this vibrant research field. Particular emphasis is put on hybrid plasmonic metasurfaces comprising organic materials and on concepts related to switchable surfaces, light-to-heat conversion, and hybridized light-matter states based on strong coupling. Funding agencies: Wenner-Gren Foundations; Swedish Research CouncilSwedish Research Council; Swedish Foundation for Strategic ResearchSwedish Foundation for Strategic Research; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linko

Ag nanoparticles (NPs) are deposited on BiVO4 photoanodes to study their effect on the photoelectrochemical (PEC) water splitting performance of the semiconductor. 15 nm light-absorbing NPs and 65 ...

Electrochromic displays based on conducting polymers exhibit higher contrasts and are cheaper, faster, more durable, and easier to synthesize as well as to process than their non-polymeric counterparts. However, current devices are typically based on thin electrochromic layers on top of a reflecting surface, which limits the thickness of the polymer layer to a few hundred nanometers. Here, we embed a light-scattering material within the electrochromic material to achieve a freestanding electrochromic paper-like electrode (50 to 500 μm). The device is based on a cellulose composite combining PEDOT:PSS as the electrochromic material and TiO2 nanoparticles as the reflecting material. Owing to the excellent refractive properties of TiO2, this nanocomposite is white in the neutral state and, when reduced, turns blue resulting in a color contrast around 30. The composite has a granular morphology and, as shown by AFM, an intermingling of TiO2 and PEDOT:PSS at the surface. Variation of the amount of TiO2 within the composite material is shown to result in a trade-off in optical and electrical properties. A proof-of-concept freestanding electrochromic device was fabricated by casting all layers successively to maximize the interlayer conformation. This freestanding device was found to be stable for over 100 cycles when ramped between 3 and −3 V.

Fast and reversible modulation of ion flow through nanosized apertures is important for many nanofluidic applications, including sensing and separation systems. Here, we present the first demonstration of a reversible plasmon-controlled nanofluidic valve. We show that plasmonic nanopores (solid-state nanopores integrated with metal nanocavities) can be used as a fluidic switch upon optical excitation. We systematically investigate the effects of laser illumination of single plasmonic nanopores and experimentally demonstrate photoresistance switching where fluidic transport and ion flow are switched on or off. This is manifested as a large (∼ 1-2 orders of magnitude) increase in the ionic nanopore resistance and an accompanying current rectification upon illumination at high laser powers (tens of milliwatts). At lower laser powers, the resistance decreases monotonically with increasing power, followed by an abrupt transition to high resistances at a certain threshold power. A similar rapid transition, although at a lower threshold power, is observed when the power is instead swept from high to low power. This hysteretic behavior is found to be dependent on the rate of the power sweep. The photoresistance switching effect is attributed to plasmon-induced formation and growth of nanobubbles that reversibly block the ionic current through the nanopore from one side of the membrane. This explanation is corroborated by finite-element simulations of a nanobubble in the nanopore that show the switching and the rectification.

The conversion of light to electrical and chemical energy has the potential to provide meaningful advances to many aspects of daily life, including the production of energy, water purification, and optical sensing. Recently, plasmonic nanoparticles (PNPs) have been increasingly used in artificial photosynthesis (e.g., water splitting) devices in order to extend the visible light utilization of semiconductors to light energies below their band gap. These nanoparticles absorb light and produce hot electrons and holes that can drive artificial photosynthesis reactions. For n-type semiconductor photoanodes decorated with PNPs, hot charge carriers are separated by a process called hot electron injection (HEI), where hot electrons with sufficient energy are transferred to the conduction band of the semiconductor. An important parameter that affects the HEI efficiency is the nanoparticle composition, since the hot electron energy is sensitive to the electronic band structure of the metal. Alloy PNPs are of particular importance for semiconductor/PNPs composites, because by changing the alloy composition their absorption spectra can be tuned to accurately extend the light absorption of the semiconductor. This work experimentally compares the HEI efficiency from Ag, Au, and Ag/Au alloy nanoparticles to TiO2 photoanodes for the photoproduction of hydrogen. Alloy PNPs not only exhibit tunable absorption but can also improve the stability and electronic and catalytic properties of the pure metal PNPs. In this work, we find that the Ag/Au alloy PNPs extend the stability of Ag in water to larger applied potentials while, at the same time, increasing the interband threshold energy of Au. This increasing of the interband energy of Au suppresses the visible-light-induced interband excitations, favoring intraband excitations that result in higher hot electron energies and HEI efficiencies.

We demonstrate scalable, low-cost and low-temperature (Funding agencies: Ministry of Higher Education and Scientific Research, Khartoum-Sudan [700]; Wenner-Gren Foundations; Swedish Government Strategic Research Area in Materials Science on Functional Material at Linkoping University [2009 00971]; Swedish Foundation for Strate

The conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) has shown promise as air electrode in renewable energy technologies like metal-air batteries and fuel cells. PEDOT is based on atomic elements of high abundance and is synthesized at low temperature from solution. The mechanism of oxygen reduction reaction (ORR) over chemically polymerized PEDOT: Cl still remains controversial with eventual role of transition metal impurities. However, regardless of the mechanistic route, we here demonstrate yet another key active role of PEDOT in the ORR mechanism. Our study demonstrates the decoupling of conductivity (intrinsic property) from electrocatalysis (as an extrinsic phenomenon) yielding the evidence of doping of the polymer by oxygen during ORR. Hence, the PEDOT electrode is electrochemically reduced (undoped) in the voltage range of ORR regime, but O-2 keeps it conducting; ensuring PEDOT to act as an electrode for the ORR. The interaction of oxygen with the polymer electrode is investigated with a battery of spectroscopic techniques. Funding Agencies|European Research Council (ERC) [307596]; Knut and Alice Wallenberg foundation; Wenner-Gren Foundations; Swedish Research Council; Swedish Foundation for Strategic Research [0-3D]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009 00971]

In recent years there has been a growing interest in the use of plasmonic nanostructures for color generation, a technology that dates back to ancient times. Plasmonic structural colors have several attractive features but once the structures arc prepared the colors arc normally fixed. Lately, several concepts have emerged for actively tuning the colors, which opens up for many new potential applications, the most obvious being novel color displays. In this review we summarize recent progress in active control of plasmonic colors and evaluate them with respect to performance criteria for color displays. It is suggested that actively controlled plasmonic colors are generally less interesting for emissive displays but could be useful for new types of electrochromic devices relying on ambient light (electronic paper). Furthermore, there are several other potential applications such as images to be revealed on demand and colorimetric sensors. Funding Agencies|Swedish Foundation for Strategic Research [EM16-0002]

Long DNA molecules can self-entangle into knots. Experimental techniques for observing such DNA knots (primarily gel electrophoresis) are limited to bulk methods and circular molecules below 10 kilobase pairs in length. Here, we show that solid-state nanopores can be used to directly observe individual knots in both linear and circular single DNA molecules of arbitrary length. The DNA knots are observed as short spikes in the nanopore current traces of the traversing DNA molecules and their detection is dependent on a sufficiently high measurement resolution, which can be achieved using high-concentration LiCl buffers. We study the percentage of molecules with knots for DNA molecules of up to 166 kilobase pairs in length and find that the knotting occurrence rises with the length of the DNA molecule, consistent with a constant knotting probability per unit length. Our experimental data compare favourably with previous simulation-based predictions for long polymers. From the translocation time of the knot through the nanopore, we estimate that the majority of the DNA knots are tight, with remarkably small sizes below 100 nm. In the case of linear molecules, we also observe that knots are able to slide out on application of high driving forces (voltage).

Arrays of gold-coated nanodomes were fabricated on glass substrates using a soft nanoimprint lithography technique. Optical transmission measurements revealed complex plasmonic resonances that proved highly sensitive to the array dimensions, the thickness of the gold layer, and the refractive index of the surrounding medium. As one promising application for these structures, the refractive index sensing capabilities of the nanodome arrays were assessed.

A nanoplasmonic biosensor chip with integrated electrical detection is presented. The concept is based on the local refractive index sensitivity of nanoplasmonic gold nanodisks (110 nm in diameter and 20 nm in height) that are fabricated, through a parallel method, directly on an array of silicon solar cells or photoactive diodes. The nanoplasmonic properties of the sensor chip were investigated both optically and electrically, with excellent agreement between the two. We show that local changes in the refractive index of the surrounding environment gives changes in the nanoplasmonic properties of the gold nanodisks, which induce corresponding changes in the photocurrent at single wavelengths of the nanoplasmonic solar cells. With a simple light-emitting diode as light source, and together with a material-specific modification protocol, the photocurrent output of the nanoplasmonic sensor chip was successfully used to monitor a specific biorecognition reaction in real-time.

A supported lipid bilayer (SLB) was formed in a microfluidic channel by vesicle fusion. The SLB, formed on a flat part of the surface, was driven by the shear forces of a bulk flow above the SLB to a part of the surface with embedded submicrometer wells. When using a bulk solution with a pH of 9.5 the advancing lipid bilayer sealed the wells, creating free-spanning membranes, whereas at a pH of 8.0 the SLB instead followed the contour of the wells.

We show that aligned gold nanotube arrays capable of supporting plasmonic resonances can be used as high performance refractive index sensors in biomolecular binding reactions. A methodology to examine the sensing ability of the inside and outside walls of the nanotube structures is presented. The sensitivity of the plasmonic nanotubes is found to increase as the nanotube walls are exposed, and the sensing characteristic of the inside and outside walls is shown to be different. Finite element simulations showed good qualitative agreement with the observed behavior. Free standing gold nanotubes displayed bulk sensitivities in the region of 250 nm per refractive index unit and a signal-to-noise ratio better than 1000 upon protein binding which is highly competitive with state-of-the-art label-free sensors.

A combination of material-specific surface chemistry, sequence-specific DNA hybridization, and size exclusion on the nanometer scale can be combined for high-precision self-assembly of lipid vesicles (see figure) to localized surface-plasmon-resonance-active nanoholes in thin Au films on SiO2.

This paper presents the use of the localized surface plasmon resonance (LSPR) sensor concept to probe the formation of macroscopic and laterally mobile supported lipid bilayers (SLBs) on SiOx-encapsulated nanohole-containing Au and Ag films. A comparison between Au- and Ag-based sensor templates demonstrates a higher sensitivity for Au-based templates with respect to both bulk and interfacial refractive index (RI) changes in aqueous solution. The lateral mobility of SLBs formed on the SiOx-encapsulated nanohole templates was analyzed using fluorescence recovery after photobleaching (FRAP), demonstrating essentially complete (>96%) recovery, but a reduction in diffusivity of about 35% compared with SLBs formed on flat SiOx substrates. Furthermore, upon SLB formation, the temporal variation in extinction peak position of the LSPR active templates display a characteristic shape, illustrating what, to the best of our knowledge, is the first example where the nanoplasmonic concept is shown capable of probing biomacromolecular structural changes without the introduction of labels. With a signal-to-noise ratio better than 500 upon protein binding to the cell-membrane mimics, the sensor concept is also proven competitive with state-of-the-art label-free sensors. (Less)

With the aim of developing a DNA sequencing methodology, we theoretically examine the feasibility of using nanoplasmonics to control the translocation of a DNA molecule through a solid-state nanopore and to read off sequence information using surface-enhanced Raman spectroscopy. Using molecular dynamics simulations, we show that high-intensity optical hot spots produced by a metallic nanostructure can arrest DNA translocation through a solid-state nanopore, thus providing a physical knob for controlling the DNA speed. Switching the plasmonic field on and off can displace the DNA molecule in discrete steps, sequentially exposing neighboring fragments of a DNA molecule to the pore as well as to the plasmonic hot spot. Surface-enhanced Raman scattering from the exposed DNA fragments contains information about their nucleotide composition, possibly allowing the identification of the nucleotide sequence of a DNA molecule transported through the hot spot. The principles of plasmonic nanopore sequencing can be extended to detection of DNA modifications and RNA characterization. Funding Agencies|National Institutes of Health [R01-HG007406, P41-RR005969]; National Science Foundation [DMR-0955959]; Wenner-Gren Foundations; Netherlands Organisation for Scientific Research; XSEDE Allocation Grant [MCA05S028]

Nanopores enable label-free detection and analysis of single biomolecules. Here, we investigate DNA translocations through a novel type of plasmonic nanopore based on a gold bowtie nanoantenna with a solid-state nanopore at the plasmonic hot spot. Plasmonic excitation of the nanopore is found to influence both the sensor signal (nanopore ionic conductance blockade during DNA translocation) and the process that captures DNA into the nanopore, without affecting the duration time of the translocations. Most striking is a strong plasmon-induced enhancement of the rate of DNA translocation events in lithium chloride (LiCl, already 10-fold enhancement at a few mW of laser power). This provides a means to utilize the excellent spatiotemporal resolution of DNA interrogations with nanopores in LiCl buffers, which is known to suffer from low event rates. We propose a mechanism based on plasmon-induced local heating and thermophoresis as explanation of our observations.

In recent years, the concept of nanopore sensing has matured from a proof-of-principle method to a widespread, versatile technique for the study of biomolecular properties and interactions. While traditional nanopore devices based on a nanopore in a single layer membrane supported on a silicon chip can be rapidly fabricated using standard microfabrication methods, chips with additional insulating layers beyond the membrane region can provide significantly lower noise levels, but at the expense of requiring more costly and time-consuming fabrication steps. Here we present a novel fabrication protocol that overcomes this issue by enabling rapid and reproducible manufacturing of low-noise membranes for nanopore experiments. The fabrication protocol, termed trans-chip illumination lithography, is based on illuminating a membrane-containing wafer from its backside such that a photoresist (applied on the wafer’s top side) is exposed exclusively in the membrane regions. Trans-chip illumination lithography permits the local modification of membrane regions and hence the fabrication of nanopore chips containing locally patterned insulating layers. This is achieved while maintaining a well-defined area containing a single thin membrane for nanopore drilling. The trans-chip illumination lithography method achieves this without relying on separate masks, thereby eliminating time-consuming alignment steps as well as the need for a mask aligner. Using the presented approach, we demonstrate rapid and reproducible fabrication of nanopore chips that contain small.12 m 12 m/ free-standing silicon nitride membranes surrounded by insulating layers. The electrical noise characteristics of these nanopore chips are shown to be superior to those of simpler designs without insulating layers and comparable in quality to more complex designs that are more challenging to fabricate. (Some figures may appear in colour only in the online journal)

This chapter aims to give an overview of how to optimize the performance of nanoplasmonic sensors. Specific biosensing challenges beyond the capability of current nanoplasmonic sensors will be discussed. Various methods to improve sensor performance will then be introduced, including solving issues related to surface chemistry. We distinguish the concept of signal enhancement, which is related to the choice of nanostructure and surface functionalization, from the concept of noise minimization, which is related to the spectroscopy techniques employed. The concepts of bulk sensitivity, figure of merit, nanostructure performance, and their relation to detection limit are discussed in detail.

This chapter is dedicated to nanoplasmonic sensing systems made compatible with studies of artificial cell membranes. After a short motivation to the opportunity of sensors designed for such studies to fill an existing technological gap, we introduce basic features of cell membranes and common mimics of the cell membrane that have been proven useful in various bioanalytical sensing applications. With suitable examples from the literature, subsequent sections exemplify how nanoplasmonics can be used to study different reactions that are associated with cell membranes. In particular, focus is on unique possibilities provided by different types of nanoplasmonic structures. For example, while discrete nanoplasmonic particles can be used as mobile probes attached to cell membranes, conductive nanoplasmonic hole structures can be used for combined optical and electrical transduction. Examples on how the latter possibility has enabled cell membrane-related reactions to be investigated with nanoplasmonic sensing combined with quartz crystal microbalance with dissipation monitoring are presented. Another key aspect of nanoplasmonic structures is that the plasmonic field (and hence the refractive index sensitivity) is strongest at the sensor surface and decays rapidly away from the surface. We describe how this feature provides a means to monitor structural changes of molecules on the surface, such as the spontaneous rupture of lipid vesicles into a supported lipid bilayer on silicon oxide-coated nanoplasmonic holes.

The resonance conditions for excitation of propagating surface plasmons at planar metal/dielectric interfaces and localized surface plasmons associated with metal nanostructures are both sensitive to changes in the interfacial refractive index. This has made these phenomena increasingly popular as transducer principles in label-free sensing of biomolecular recognition reactions. In this article, the authors review the recent progress in the field of nanoplasmonic bioanalytical sensing in general, but set particular focus on certain unique possibilities provided by short-range ordered nanoholes in thin metal films. Although the latter structures are formed in continuous metal films, while nanoparticles are discrete entities, these two systems display striking similarities with respect to sensing capabilities, including bulk sensitivities, and the localization of the electromagnetic fields. In contrast, periodic arrays of nanoholes formed in metal films, most known for their ability to provide wavelength-tuned enhanced transmission, show more similarities with conventional propagating surface plasmon resonance. However, common for both short-range ordered and periodic nanoholes formed in metal films is that the substrate is electrically conductive. Some of the possibilities that emerge from sensor templates that are both electrically conductive and plasmon active are discussed and illustrated using recent results on synchronized nanoplasmonic and quartz crystal microbalance with dissipation monitoring of supported lipid bilayer formation and subsequent biomolecular recognition reactions. Besides the fact that this combination of techniques provides an independent measure of biomolecular structural changes, it is also shown to contribute with a general means to quantify the response from nanoplasmonic sensors in terms of bound molecular mass.

The revelation of protein-protein interactions is one of the main preoccupations in the field of proteomics. Nanoplasmonics has emerged as an attractive surface-based technique because of its ability to sense protein binding under physiological conditions in a label-free manner. Here, we use short-range ordered holes with a diameter of approximately 150 nm and a depth of approximately 50 nm as a nanoplasmonic template. A approximately 40 nm high cylindrical region of Au is exposed on the walls of the holes only, while the rest of the surface consists of TiO2. Since the sensitivity is confined to the nanometric holes, the use of two different materials for the sensor substrate offers the opportunity to selectively bind proteins to the most sensitive Au regions on the sensor surface. This was realized by applying material-selective poly(ethylene glycol)-based surface chemistry, restricting NeutrAvidin binding to surface-immobilized biotin on the Au areas only. We show that under mass-transport limited conditions (low nM bulk concentrations), the initial time-resolved response of uptake could be increased by a factor of almost 20 compared with the case where proteins were allowed to bind on the entire sensor surface and stress the generic relevance of this concept for nanoscale sensors. In the scope of further optimizing the limit of detection (LOD) of the sensor structure, we present finite-element (FE) simulations to unravel spatially resolved binding rates. These revealed that the binding rates in the holes occur in a highly inhomogeneous manner with highest binding rates observed at the upper rim of the holes and the lowest rates observed at the bottom of the holes. By assuming a plasmonic field distribution with enhanced sensitivity at the Au-TiO2 interface, the FE simulations reproduced the experimental findings qualitatively.

Nanoplasmonic sensors based on short-range ordered nanoholes in thin metal films and discrete metal nanoparticles are known to provide similar sensing performance. However, a perforated metal film is unique in the sense that the holes can be designed to penetrate through the substrate, thereby also fulfilling the role of nanofluidic channels. This paper presents a bioanalytical sensing concept based on short-range ordered nanoplasmonic pores (diameter 150 nm) penetrating through a thin (around 250 nm) multilayer membrane composed of gold and silicon nitride (SiN) that is supported on a Si wafer. Also, a fabrication scheme that enables parallel production of multiple (more than 50) separate sensor chips or more than 1000 separate nanoplasmonic membranes on a single wafer is presented. Together with the localization of the sensitivity to within such short-range ordered nanoholes, the structure provides a two-dimensional nanofluidic network, sized in the order of 100 x 100 microm(2), with nanoplasmon active regions localized to each individual nanochannel. A material-specific surface-modification scheme was developed to promote specific binding of target molecules on the optically active gold regions only, while suppressing nonspecific adsorption on SiN. Using this protocol, and by monitoring the temporal variation in the plasmon resonance of the structure, we demonstrate flow-through nanoplasmonic sensing of specific biorecognition reactions with a signal-to-noise ratio of around 50 at a temporal resolution below 190 ms. With flow, the uptake was demonstrated to be at least 1 order of magnitude faster than under stagnant conditions, while still keeping the sample consumption at a minimum.

We present a method providing synchronized measurements using the two techniques: quartz crystal microbalance with dissipation (QCM-D) monitoring and localized surface plasmon resonance (LSPR). This was achieved by letting a thin gold film perforated with short-ranged ordered plasmon-active nanoholes act as one of the electrodes of a QCM-D crystal. This enabled transmission-mode optical spectroscopy to be used to temporally resolve colorimetric changes of the LSPR active substrate induced upon biomolecular binding events. The LSPR response could thus be compared with simultaneously obtained changes in resonance frequency, Deltaf, and energy dissipation, DeltaD, of the QCM-D device. Since the LSPR technique is preferentially sensitive to changes within the voids of the nanoholes, while the QCM-D technique is preferentially sensitive to reactions on the planar region between the holes, a surface chemistry providing the same binding kinetics on both gold and silica was used. This was achieved by coating the substrate with poly(L-lysine)-graft-poly(ethylene glycol) (PLL-g-PEG), which was shown to bind in the same manner on silica and gold modified with a carboxyl-terminated thiol. In this way, the combined setup provided new information about structural changes upon PLL-g-PEG adsorption. We also demonstrate subsequent binding of NeutrAvidin and an immunoreaction utilizing biotin-modified IgG. The combined information from the synchronized measurements was also used in a new way to estimate the sensing volume of the LSPR sensor.

One of the primary advantages of nanoscale sensors is that they often can provide conceptually new ways of performing sensing that are not feasible with their large-scale analogs. For example, the small size of nanoscale sensor elements, such as plasmonic metal nanoparticles, allows them to be combined with nanofluidic systems. Among the potential applications of such a combination is the efficient delivery of analyte to the sensor surface. With this in mind, in this work we look to address the challenge of creating and positioning nanoplasmonic sensor elements within nanofluidic pores. A scheme is presented that allows for the production of arrays of pores in a thin (220 nm) silicon nitride membrane with one plasmonic nanoparticle sensor element in each pore. The high throughput fabrication protocol is parallel and enables multiple sensor chips to be produced simultaneously, yet with accurate tuning of the dimension and shape of the nanoparticles. The presented system is shown to possess polarization-sensitive plasmonic resonances that can be tuned significantly in the visible wavelength range by just varying one process parameter. The thickness of the membrane could be optimized to minimize the influence of the optical membrane interference on the plasmonic readout. The sensitivity of the plasmon resonances to changes in refractive index, which forms the basis for using the system for biosensing, was found to be competitive with other nanoplasmonic sensors.

This article summarizes our most recent contributions to the rapidly growing field of supported lipid assemblies with emphasis on current studies addressing both fundamental and applied aspects of supported lipid bilayer (SLB) and tethered lipid vesicles (TLVs) to be utilized in sensing applications. The new insights obtained from combining the quartz crystal microbalance with dissipation monitoring technique with surface plasmon resonance are described, and we also present recent studies in which nanoplasmonic sensing has been used in studies of SLBs and TLVs. To gain full control over the spatial arrangement of TLVs in both two and three dimensions, we have developed a method for site-selective and sequence-specific sorting of DNA-tagged vesicles to surfaces modified with complementary DNA. The combination of this method with nanoplasmonic sensing formats is covered as well as the possibility of using DNA-modified vesicles for the detection of unlabeled DNA targets on the single-molecule level. Finally, a new method for membrane fusion induced by hybridization of vesicle-anchored DNA is demonstrated, including new results on content mixing obtained with vesicle populations encapsulating short, complementary DNA strands.

We present a novel cost-efficient method for the fabrication of high-quality self-aligned plasmonic nanopores by means of an optically controlled dielectric breakdown. Excitation of a plasmonic bowtie nanoantenna on a dielectric membrane localizes the high-voltage-driven breakdown of the membrane to the hotspot of the enhanced optical field, creating a nanopore that is automatically self-aligned to the plasmonic hotspot of the bowtie. We show that the approach provides precise control over the nanopore size and that these plasmonic nanopores can be used as single molecule DNA sensors with a performance matching that of TEM-drilled nanopores. The principle of optically controlled breakdown can also be used to fabricate nonplasmonic nanopores at a controlled position. Our novel fabrication process guarantees alignment of the nanopore with the optical hotspot of the nanoantenna, thus ensuring that pore-translocating biomolecules interact with the concentrated optical field that can be used for detection and manipulation of analytes.