Silver nanoparticles - laser induced graphene (Ag NPs - LIG) hybrid electrodes for sensitive electrochemical-surface enhanced Raman spectroscopy (EC-SERS) detection.

This paper presents a novel approach for the fabrication of low cost Electrochemical-Surface Enhanced Raman Scattering (EC-SERS) sensing platforms. Laser Induced Graphene (LIG) electrodes were readily fabricated by direct laser writing of polyimide tapes and functionalized with silver nanoparticles (Ag NPs) to obtain hybrid Ag NPs - LIG electrodes suitable for EC-SERS analysis. Detection was achieved by coupling a handheld potentiostat with a Raman spectrograph, enabling measurement of SERS spectra of target analytes generated during voltage sweeps in the 0.0 to -1.0 V interval range. The sensing capabilities of the fabricated system were first tested with model molecule 4-aminobenzenethiol (4-ABT). Following sensitive detection of 4-ABT, EC-SERS analysis of food contaminant melamine in milk and antibiotic difloxacin hydrochloride (DIF) in river water was demonstrated, achieving sensitive detection of both analytes without pre-treatment steps. The easiness of fabrication, versatility of design, rapid analysis time and potential miniaturization of the system make Ag NPs - LIG electrodes suitable for a large range of in situ applications in the field of food monitoring and for environmental analysis.

Direct-write formation of integrated bottom contacts to laser-induced graphene-like carbon.

We report a simple, scalable two-step method for direct-write laser fabrication of 3D, porous graphene-like carbon electrodes from polyimide films with integrated contact plugs to underlying metal layers (Au or Ni). Irradiation at high average CO2laser power (30 W) and low scan speed (∼18 mm s)-1leads to formation of 'keyhole' contact plugs through local ablation of polyimide (initial thickness 17µm) and graphitization of the plug perimeter wall. Top-surface laser-induced graphene (LIG) electrodes are then formed and connected to the plug by raster patterning at lower laser power (3.7 W) and higher scan speed (200 mm s)-1. Sheet resistance data (71 ± 15 Ω sq.)-1indicates formation of high-quality surface LIG, consistent with Raman data which yield sharp first- and second-order peaks. We have also demonstrated that high-quality LIG requires a minimum initial polyimide thickness. Capacitance data measured between surface LIG electrodes and the buried metal film indicate a polyimide layer of thickness ∼7µm remaining following laser processing. By contrast, laser graphitization of polyimide of initial thickness ∼8µm yielded devices with large sheet resistance (>1 kΩ sq.)-1. Raman data also indicated significant disorder. Plug contact resistance values were calculated from analysis of transfer line measurement data for single- and multi-plug test structures. Contacts to buried nickel layers yielded lower plug resistances (1-plug: 158 ± 7 Ω , 4-plug: 31 ± 14 Ω) compared to contacts to buried gold (1-plug: 346 ± 37 Ω , 4-plug: 52 ± 3 Ω). Further reductions are expected for multi-plug structures with increased areal density. Proof-of-concept mm-scale LIG electrochemical devices with local contact plugs yielded rapid electron transfer kinetics (rate constantk0 âˆ¼ 0.017 cm s-1), comparable to values measured for exposed Au films (k0 âˆ¼0.023 cm s)-1. Our results highlight the potential for integration of LIG-based sensor electrodes with semiconductor or roll-to-roll manufacturing.

A Smart Archive Box for Museum Artifact Monitoring Using Battery-Less Temperature and Humidity Sensing.

For the first time, this paper reports a smart museum archive box that features a fully integrated wireless powered temperature and humidity sensor. The smart archive box has been specifically developed for microclimate environmental monitoring of stored museum artifacts in cultural heritage applications. The developed sensor does not require a battery and is wirelessly powered using Near Field Communications (NFC). The proposed solution enables a convenient means for wireless sensing with the operator by simply placing a standard smartphone in close proximity to the cardboard archive box. Wireless sensing capability has the advantage of enabling long-term environmental monitoring of the contents of the archive box without having to move and open the box for reading or battery replacement. This contributes to a sustainable preventive conservation strategy and avoids the risk of exposing the contents to the external environment, which may result in degradation of the stored artifacts. In this work, a low-cost and fully integrated NFC sensor has been successfully developed and demonstrated. The developed sensor is capable of wirelessly measuring temperature and relative humidity with a mean error of 0.37 °C and ±0.35%, respectively. The design has also been optimized for low power operation with a measured peak DC power consumption of 900 µW while yielding a 4.5 cm wireless communication range. The power consumption of the NFC sensor is one of the lowest found in the literature. To the author's knowledge, the NFC sensor proposed in this paper is the first reporting of a smart archive box that is wirelessly powered and uniquely integrated within a cardboard archive box.

Gate-controlled heat generation in ZnO nanowire FETs.

Nanoscale heating production using nanowires has been shown to be particularly attractive for a number of applications including nanostructure growth, localized doping, transparent heating and sensing. However, all proof-of-concept devices proposed so far relied on the use of highly conductive nanomaterials, typically metals or highly doped semiconductors. In this article, we demonstrate a novel nanoheater architecture based on a single semiconductor nanowire field-effect transistor (NW-FET). Nominally undoped ZnO nanowires were incorporated into three-terminal devices whereby control of the nanowire temperature at a given source-drain bias was achieved by additional charge carriers capacitatively induced via the third gate electrode. Joule-heating selective ablation of poly(methyl methacrylate) deposited on ZnO nanowires was shown, demonstrating the ability of the proposed NW-FET configuration to enhance by more than one order of magnitude the temperature of a ZnO nanowire, compared to traditional two-terminal configurations. These findings demonstrate the potential of field-effect architectures to improve Joule heating power in nanowires, thus vastly expanding the range of suitable materials and applications for nanowire-based nanoheaters.

Plasmonic detection of mercury via amalgam formation on surface-immobilized single Au nanorods.

Au nanorods were used as plasmonic transducers for investigation of mercury detection through a mechanism of amalgam formation at the nanorod surfaces. Marked scattering color transitions and associated blue shifts of the surface plasmon resonance peak wavelengths (λmax) were measured in individual nanorods by darkfield microscopy upon chemical reduction of Hg(II). Such changes were related to compositional changes occurring as a result of Hg-Au amalgam formation as well as morphological changes in the nanorods' aspect ratios. The plot of λmax shifts vs. Hg(II) concentration showed a linear response in the 10-100 nM concentration range. The sensitivity of the system was ascribed to the narrow width of single nanorod scattering spectra, which allowed accurate determination of peak shifts. The system displayed good selectivity as the optical response obtained for mercury was one order of magnitude higher than the response obtained with competitor ions. Analysis of mercury content in river and tap water were also performed and highlighted both the potential and limitation of the developed method for real sensing applications.

Hot-electron injection in Au nanorod-ZnO nanowire hybrid device for near-infrared photodetection.

In this Letter, we present a new class of near-infrared photodetectors comprising Au nanorods-ZnO nanowire hybrid systems. Fabricated hybrid FET devices showed a large photoresponse under radiation wavelengths between 650 and 850 nm, accompanied by an "ultrafast" transient with a time scale of 250 ms, more than 1 order of magnitude faster than the ZnO response under radiation above band gap. The generated photocurrent is ascribed to plasmonic-mediated generation of hot electrons at the metal-semiconductor Schottky barrier. In the presented architecture, Au-nanorod-localized surface plasmons were used as active elements for generating and injecting hot electrons into the wide band gap ZnO nanowire, functioning as a passive component for charge collection. A detailed investigation of the hot electron generation and injection processes is discussed to explain the improved and extended performance of the hybrid device. The quantum efficiency measured at 650 nm was calculated to be approximately 3%, more than 30 times larger than values reported for equivalent metal/semiconductor planar photodetectors. The presented work is extremely promising for further development of novel miniaturized, tunable photodetectors and for highly efficient plasmonic energy conversion devices.

Facile formation of ordered vertical arrays by droplet evaporation of Au nanorod organic solutions.

Droplet evaporation is a simple method to induce organization of Au nanorods into ordered superstructures. In general, the self-assembly process occurs by evaporation of aqueous suspensions under strictly controlled experimental conditions. Here we present formation of large area ordered vertical arrays by droplet evaporation of Au nanorod organic suspensions. The uncontrolled (free air) evaporation of such suspensions yielded to formation of ordered nanorod domains covering the entire area of a 5 mm diameter droplet. Detailed investigation of the process revealed that nanorods organized into highly ordered vertical domains at the interface between solvent and air on a fast time scale (minutes). The self-assembly process mainly depended on the initial concentration of nanorod solution and required minimal control of other experimental parameters. Nanorod arrays displayed distinct optical properties which were analyzed by optical imaging and spectroscopy and compared to results obtained from theoretical calculations. The potential use of synthesized arrays as surface-enhanced Raman scattering probes was demonstrated with the model molecule 4-aminobenzenthiol.

Synthesis, optical properties and alignment of poly(9,9-dioctylfuorene) nanofibers.

Poly(9,9-dioctlylfluorene) (PFO) nanofibers were fabricated by solution template wetting of anodic alumina membranes. Nanofibers with controlled thickness of 23 nm and length between 0.8 and 10 µm, were obtained, regulated by the dimensions of the used template. Nanofibers displayed spectroscopic characteristics associated with the formation of significant percentages of planar and elongated ß phase within the amorphous PFO glassy-phase. Optical polarized microscopy displayed high birefringence resulting from the high degree of internal order induced by ß phase generation within the fibers. The structural intra-chain reorganization associated with formation of ß phase was promoted by the strong geometrical confinement imposed on the material by the porous template during polymer wetting and solvent evaporation. Flow and shear force alignment techniques were used to control the orientation of fabricated PFO nanofibers, yielding to formation of large oriented nanofiber arrays on transparent substrates.

Highly polarized luminescence from ß-phase-rich poly(9,9-dioctylfluorene) nanofibers.

Novel poly(9,9-dioctlylfluorene) (PFO) nanofibers were fabricated by solution template wetting of anodic aluminum oxide (AAO) templates with a pore diameter of 25 nm. Individual nanofibers displayed a pronounced axially polarized luminescence with a typical emission dichroic ratio of 15 and low spread of the emissive species angular distribution. The strong optical characteristics were ascribed to intrachain reorientation of amorphous PFO to a more planar and elongated ß-phase conformation induced by mechanical strain during polymer template pore infiltration. Absorption optical spectroscopy on nanofiber mats confirmed formation of 24% ß-phase emissive segments, which dominated the nanofiber luminescence characteristics. X-ray diffraction measurements were used to confirm and quantify the extent of nanofiber internal molecular alignment.

X-ray fluorescence analysis of three late medieval silver chalices associated with Ireland.

This paper presents the results of the first X-ray fluorescence (XRF) investigation conducted on three late medieval chalices associated with Ireland: the Ó Learghusa chalice, auctioned as medieval Irish in 2021, does not have a confirmed provenance; the de Burgo-O'Malley chalice, dated 1494, and the TP-IEP chalice, dated 1589, both of Irish provenance. This study effectively addressed the knowledge gap concerning Irish medieval silver chalices composition. The analysis revealed that both the Ó Learghusa and de Burgo-O'Malley chalices were crafted from a silver-copper alloy and adorned using a fire-gilding technique. The blue and green enamels on the de Burgo-O'Malley chalice were found to be constituted by cobalt and iron/copper glasses, respectively. In contrast, the TP-IEP chalice exhibited a more intricate structure, being a composite object with partial silver gilt and with the bowl and base possibly made of a ternary silver-copper-gold alloy. The TP-IEP chalice's knop displayed glass, simulating gems with transparent, blue, and purple colorations. XRF analysis allowed identification of lead-potash glass, while the red glass displayed a rich iron content and was identified as soda-lime glass. The analysis allowed concluding that the de Burgo-O'Malley chalice had retained its original condition, including its original gilding and enamels, while the Ó Learghusa and TP-IEP chalices appeared to have undergone refurbishment. These significant discoveries contribute to a deeper understanding of the historical context and artistic craftsmanship behind these late medieval chalices, shedding light on their unique stories within Irish art and history. Supplementary Information: The online version contains supplementary material available at 10.1186/s40494-024-01240-2.

Pen direct writing of SERRS-based lateral flow assays for detection of penicillin G in milk.

Direct pen writing offers versatile opportunities for development of low-cost tests for point-of-care applications. In this work a lateral flow immunoassay (LFIA) test was fabricated by hand "writing" immunoprobes onto hand-cut nitrocellulose strips with a commercial fountain pen. The qualitative capabilities of the test were extended by addition of a Raman reporter and consequent design and fabrication of a Surface Enhanced Resonant Raman Scattering (SERRS)-LFIA test. As proof-of-concept, dual detection of penicillin G was achieved in milk with a visual LOD of 20 ppm and a dynamic range of 0.03-97.5 ppm. Evaluation against equivalent tests performed with conventionally prepared LFIA strips showed comparable results, thus demonstrating the validity of the test. These results demonstrate the potential for further decrease in cost and consequent broader use of LFIA tests in remote regions and resource-limited environments.

Direct Laser Writing of Chitosan-Borax Composites: Toward Sustainable Electrochemical Sensors.

In this study, the laser-induced graphitization process of sustainable chitosan-based formulations was investigated. In particular, optimal lasing conditions were investigated alongside the effect of borax concentration in the chitosan matrix. In all cases, it was found that the obtained formulations were graphitizable with a CO2 laser. This process gave rise to the formation of high surface area, porous, and electrically conductive laser-induced graphene (LIG) structures. It was found that borax, as a cross-linker of chitosan, enabled the graphitization process when its content was ≥30 wt % in the chitosan matrix, allowing the formation of an LIG phase with a significant content of graphite-like structures. The graphitization process was investigated by thermogravimetric analysis (TGA), Raman, X-ray photoemission (XPS), and Fourier transform infrared (FTIR) spectroscopies. LIG electrodes obtained from CS/40B formulations displayed a sheet resistance as low as 110 Ω/sq. Electrochemical characterization was performed after a 10 min electrode activation by cycling in 1 M KCl. A heterogeneous electron transfer rate, k0, of 4 × 10-3 cm s-1 was determined, indicating rapid electron transfer rates at the electrode surface. These results show promise for the introduction of a new class of sustainable composites for LIG electrochemical sensing platforms.

Establishing the original order of the poems in Harward's Almanac using paleography, codicology, X-ray fluorescence spectroscopy, and statistical analysis.

This work presents the results of a transdisciplinary analysis performed on Harward's Almanac (Dublin, 1666), an extremely rare volume currently housed in the National Library of Ireland. The uniqueness and historical value of the Almanac is related to the presence of nineteen handwritten poems, entered by an anonymous scribe. These record textually important English clandestine satire circulating anonymously in Dublin in the late seventeenth and early eighteenth century. Following a comprehensive historical assessment, it appeared evident that the current order of leaves was incorrect. To reconstruct the correct order of the leaves, and hence the likely sequence in which the manuscript poems were inscribed, this study employed a codicological/paleographic analysis complemented by analytical (X-ray fluorescence, XRF) and statistical (Self Organizing Map, SOM) investigation. Specifically, point XRF analysis was carried out for each handwritten page of the Almanac, allowing identification of ink elemental compositions (iron-based ink) and successfully supporting the validity of historical hypotheses on the poems' order of inscription. The statistical organization of XRF data by SOMs allowed easy bi-dimensional visualization of the data set (54 points) and identification of ink similarities, once more validating the historical assessment. Supplementary Information: The online version contains supplementary material available at 10.1186/s40494-023-01107-y.

Electrochemical sensor for enzymatic lactate detection based on laser-scribed graphitic carbon modified with platinum, chitosan and lactate oxidase.

We developed a flexible laser scribed graphitic carbon based lactate biosensor fabricated using a low cost 450 nm laser. We demonstrated a facile fabrication method involving electrodeposition of platinum followed by two casting steps for modification with chitosan and lactate oxidase. The biosensor demonstrated chronoamperometric lactate detection within a linear range from 0.2 mM to 3 mM, (R2 > 0.99), with a limit of detection of 0.11 mM and a sensitivity of 35.8 µA/mM/cm2. The biosensor was successful in performing up to 10 consecutive measurements (one after the other) indicating good working stability (RSD <5%). Concerning storage stability, there was no decrease in signal response after 30 days of storage at 4 °C. Additionally, we demonstrate enzymatic lactate detection whilst the flexible polyimide substrates were fixed at a curvature (K) of 0.14 mm-1. No noticeable change in signal response was observed in comparison to calibrations obtained at a curvature of 0 mm-1, signifying potential opportunities for sensor attachment or integration with oral-care products such as mouth swabs. Both laser scribed graphitic carbon and Ag/AgCl modified-laser scribed graphitic carbon were successful as reference electrodes for chronoamperometric lactate measurements. Furthermore, using a three-electrode configuration on polyimide, lactate detection in both artificial saliva and sterile human serum samples was achieved for two spiked concentrations (0.5 mM and 1 mM).

Highly Sensitive and Ultra-Responsive Humidity Sensors Based on Graphene Oxide Active Layers and High Surface Area Laser-Induced Graphene Electrodes.

Ultra-sensitive and responsive humidity sensors were fabricated by deposition of graphene oxide (GO) on laser-induced graphene (LIG) electrodes fabricated by a low-cost visible laser scribing tool. The effects of GO layer thickness and electrode geometry were investigated. Sensors comprising 0.33 mg/mL GO drop-deposited on spiral LIG electrodes exhibited high sensitivity up to 1800 pF/% RH at 22 °C, which is higher than previously reported LIG/GO sensors. The high performance was ascribed to the high density of the hydroxyl groups of GO, promoted by post-synthesis sonication treatment, resulting in high water physisorption rates. As a result, the sensors also displayed good stability and short response/recovery times across a wide tested range of 0-97% RH. The fabricated sensors were benchmarked against commercial humidity sensors and displayed comparable performance and stability. Finally, the sensors were integrated with a near-field communication tag to function as a wireless, battery-less humidity sensor platform for easy read-out of environmental humidity values using smartphones.

Enhanced thermal and ultrasonic stability of a fungal protease encapsulated within biomimetically generated silicate nanospheres.

BACKGROUND: Dendrimers are highly branched synthetic macromolecules with a globular shape. They have been successfully used for generation of nanospheres at mild conditions via biomimetic silicification. Encapsulation of enzyme molecules within these nanospheres during their synthesis is a promising method for rapid and efficient entrapment of several enzymes. However, encapsulation of proteolytic enzymes has been rarely done via biomimetic silicification. As well, the operational stability of encapsulated enzyme has not been systematically reported. METHODS: A proteolytic enzyme, either alpha-Chymotrypsin or a fungal protease from Aspergilus Oryzea was encapsulated along with iron oxide nanoparticles within particles yielded via biomimetic silicification of different generations of polyamidoamine (PAMAM) dendrimers. Stability of encapsulated enzyme was compared to that of free enzyme during storage at room temperature. As well, their thermal and ultrasonic stabilities were measured. Scanning electron microscopy, transmission electron microscopy and optical microscopy were used to investigate the morphology of nanospheres. RESULTS: Determination of encapsulation efficiency revealed that approximately 85% of fungal protease with concentration 1.4mg mL(-1) stock solution was immobilized within particles yielded by generation 0. Based on microscopic images the generated particles interconnected with each other and had spherical morphologies independent of generation. Kinetic analysis of encapsulated fungal protease demonstrated that Mechaelis-Menten constant (K(m)) slightly increased. CONCLUSION: PAMAM dendrimer generation 0 could be effectively used for rapid encapsulation of a fungal protease from Aspegilus Oryzae. GENERAL SIGNIFICANCE: Encapsulation significantly enhances the thermal and ultrasonic stabilities of enzymes, suggesting a range of diverse applications for them.

Design of Experiments and Optimization of Laser-Induced Graphene.

Realization of graphene-based sensors and electronic devices remains challenging, in part due to integration challenges with current fabrication and manufacturing processes. Thus, scalable methods for in situ fabrication of high-quality graphene-like materials are essential. Low-cost CO2 laser engravers can be used for site-selective conversion of polyimide under ambient conditions to create 3-D, rotationally disordered, few-layer, porous, graphene-like electrodes. However, the influences of non-linear parameter terms and interactions between key parameters on the graphitization process present challenges for rapid, resource-efficient optimization. An iterative optimization strategy was developed to identify promising regions in parameter space for two key parameters, laser power and scan speed, with the goal of optimizing electrode performance while maximizing scan speed and hence fabrication throughput. The strategy employed iterations of Design of Experiments Response Surface (DoE-RS) methods combined with choices of readily measurable parameters to minimize measurement resources and time. The initial DoE-RS experiment set employed visual response parameters, while subsequent iterations used sheet resistance as the optimization parameter. The final model clearly demonstrates that laser graphitization through raster scanning is a highly non-linear process requiring polynomial terms in scan speed and laser power up to fifth order. Two regions of interest in parameter space were identified using this strategy: Region 1 represents the global minimum for sheet resistance for this laser (∼16 Ω/sq), found at a low scan speed (70 mm/s) and a low average power (2.1 W) . Region 2 is a local minimum for sheet resistance (36 Ω/sq), found at higher values for scan speed (340 mm/s) and average power (3.4 W), allowing ∼5-fold reduction in write time. Importantly, these minima do not correspond to constant ratios of average laser power to scan speed. This highlights the benefits of DoE-RS methods in rapid identification of optimum parameter combinations that would be difficult to discover using traditional one-factor-at-a-time optimization. Verification data from Raman spectroscopy showed sharp 2D peaks with mean full-width-at-half-maximum intensity values <80 cm-1 for both regions, consistent with high-quality 3D graphene-like carbon. Graphene-based electrodes fabricated using the parameters from the respective regions yielded similar performance when employed as capacitive humidity sensors with hygroscopic dielectric layers. Devices fabricated using Region 1 parameters (16 Ω/sq) yielded capacitance responses of 0.78 ± 0.04 pF at 0% relative humidity (RH), increasing to 31 ± 7 pF at 85.1% RH. Region 2 devices (36 Ω/sq) showed comparable responses (0.88 ± 0.04 pF at 0% RH, 28 ± 5 pF at 85.1% RH).

Laser Scribing Fabrication of Graphitic Carbon Biosensors for Label-Free Detection of Interleukin-6.

Interleukin-6 (IL-6) is an important immuno-modulating cytokine playing a pivotal role in inflammatory processes in disease induction and progression. As IL-6 serves as an important indicator of disease state, it is of paramount importance to develop low cost, fast and sensitive improved methods of detection. Here we present an electrochemical immunosensor platform based on the use of highly porous graphitic carbon electrodes fabricated by direct laser writing of commercial polyimide tapes and chemically modified with capture IL-6 antibodies. The unique porous and 3D morphology, as well as the high density of edge planes of the graphitic carbon electrodes, resulted in a fast heterogeneous electron transfer (HET) rate, k0 = 0.13 cm/s. The resulting immunosensor showed a linear response to log of concentration in the working range of 10 to 500 pg/mL, and low limit of detection (LOD) of 5.1 pg/mL IL-6 in phosphate buffer saline. The total test time was approximately 90 min, faster than the time required for ELISA testing. Moreover, the assay did not require additional sample pre-concentration or labelling steps. The immunosensor shelf-life was long, with stable results obtained after 6 weeks of storage at 4 °C, and the selectivity was high, as no response was obtained in the presence of another inflammatory cytokine, Interlukin-4. These results show that laser-fabricated graphitic carbon electrodes can be used as selective and sensitive electrochemical immunosensors and offer a viable option for rapid and low-cost biomarker detection for point-of-care analysis.

Ion-transfer electrochemistry at arrays of nanointerfaces between immiscible electrolyte solutions confined within silicon nitride nanopore membranes.

Ion transfer across interfaces between immiscible liquids provides a means for the nonredox electrochemical detection of ions. Miniaturization of such interfaces brings the benefits of enhanced mass transport. Here, the electrochemical behavior of geometrically regular arrays of nanoscale interfaces between two immiscible electrolyte solutions (nanoITIES arrays) is presented. These were prepared by supporting the two electrolyte phases within silicon nitride membranes containing engineered arrays of nanopores. The nanoITIES arrays were characterized by cyclic voltammetry of the interfacial transfer of tetraethylammonium cation (TEA(+)) between the aqueous phase and the gelled organic phase. Effects of pore radius, pore center-to-center separation, and number of pores in the array were examined. The ion transfer produced apparent steady-state voltammetry on the forward and reverse sweeps at all experimentally accessible scan rates and at all nanopore array designs. However, background-subtraction of the voltammograms revealed the evolution of a peak-shaped response on the reverse sweep with increasing scan rate, indicative of pores filled with the organic phase to a certain extent. The steady-state voltammetric behavior at the nanoITIES arrays on the forward sweep for arrays with significant diffusion zone overlap between adjacent nanoITIES is indicative of the dominance of radial diffusion to interfaces at the edge of the arrays over linear diffusion to interfaces within the arrays. This implies that nanoITIES arrays, which occupy an overall area of micrometer dimensions, behave like a single microITIES of corresponding area to the nanoITIES array.

Optical properties of micro-patterned silver nanoparticle substrates.

In this paper, we describe a novel technique for depositing metal nanoparticles (NPs) on a planar substrate whereby the NPs are micro-patterned on the surface by a simple stamp-printing procedure. The method exploits the attractive force between negatively charged colloidal metal NPs and positively-charged polyelectrolyte layers which have been selectively deposited on the surface. Using this technique, large uniform areas of patterned metal NPs, with different plasmonic properties, were achieved by optimisation of the stamping process. We report the observation of unusual fluorescence emission from these structures. The emission was measured using epifluorescence microscopy. Fluorescence lifetime behaviour was also measured. Furthermore, the mu-patterned NPs exhibited blinking behaviour under 469 nm excitation and the fluorescence spectrum was multi-peaked. It has been established that the fluorescence is independent of the plasmon resonance properties of the NPs. As well as optimising the novel NP mu-patterning technique, this work discusses the origin and characteristics of the anomalous fluorescence behaviour in order to characterise and minimise this unwanted background contribution in the use of metal NPs for plasmonic enhancement of fluorescence for optical biochip applications.