This PDF file contains the front matter associated with SPIE Proceedings Volume 12396, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

Raman investigations are carried out to evaluate potential real-world application fields using an in-house developed portable shifted excitation Raman difference spectroscopy (SERDS) system at 785 nm. Pilot Raman measurements are performed in the presence of background light, laser-induced fluorescence, within optically turbid media and of weak Raman scatterers i.e., ambient air gases. In the presence of background light and laser-induce fluorescence, SERDS separates Raman signals of soil substances with a 15-fold improvement of the signal-to-background noise. Ingredients of bovine milk as the optically turbid test sample are clearly detected and identified. Ambient air gases are investigated even under daylight conditions. The results show the potential of the portable SERDS sensor systems for real-world applications,

Metallic nanostructures have the potential to be used in a variety of applications related to sensing and imaging biological molecules due to their ability to enhance the way molecules absorb and emit light. However, the interaction between metallic nanostructure and molecules can give rise to difficulty with determining precise molecular positions and orientations and therefore pose major challenges in the field of super-resolution imaging. In this work, we used axially defocused imaging to analyze the interaction between a single fluorescent molecule and a metallic nanostructure. In addition, a pattern matching algorithm was used to analyze the images, explore the interaction between the molecule and the nanostructure and thereby determine the lateral position. The accuracy was found to improve while the degree was dependent on the dipolar orientation and the distance between dipole and nanostructure. This approach has the potential to improve the reliability of using metallic nanostructures for imaging and sensing in the future and opens up new possibilities for various imaging and sensing methods.

Upconversion (UC) luminescence sensing is a technique to improve the detection limit of conventional fluorescence in biosensing that is commonly limited by the autofluorescence-generated background signal. The main limitation of UC materials is their low wavelength conversion efficiency. Many studies have been made to enhance the efficiency of UC materials by optimizing light absorption and energy transfer processes. However, rather low efficiency remains an issue limiting the practical usage of UC materials in biosensors. Plasmon enhancement is a way to improve UC photoluminescence by enhancing the excitation and emission rates. In this study, we modeled and fabricated gold gratings for exciting surface plasmon polaritons (SPPs) at 976-nm wavelength. We aim at increasing the local optical intensity at the locations of UC nanoparticles on a nano-structured plasmonic surface. The UC nanoparticles were adsorbed on the gratings via biomolecule conjugation. UC photoluminescence on the gratings was compared with flat gold surfaces. Experimentally, we achieved UC enhancement up to 70, which is relatively high in comparison with other plasmon-enhanced UC techniques presented in the literature. The results of our work can be applied in various biosensing applications in which low excitation intensity is preferred.

Surface plasmon, collective electron oscillation induced by light absorption in noble metals, has received renewed attention that opens a new area of photonics research in what is known as thermoplasmonics. As thermoplasmonics develops, opto-thermal response measurement of a single nanostructure becomes essential. In this study, we propose a collection-type near-field scanning optical microscopy (NSOM) that can simultaneously measure light absorption and near-field enhancement on a single nanostructure. We analyzed light absorption from optically induced thermal expansion while measuring a near-field coupled with the NSOM tip. We have observed discrepancy and nonlinearity of angular spectrum between light absorption and near-field enhancement on gold thin films and compared with simulation results based on iterative opto-thermal analysis. We were able to determine the cause of the axial shift on the NSOM and the mechanisms by which the discrepancy may ariss. The proposed technique can also acquire optical characteristics of a single disk in a periodic array of gold nanodisks, and even measure the gaps between the disks. Furthermore, we expect the proposed technology to be extended to measuring near-field thermal characteristics of more complicated structure such as metamaterials.

We present the effects of a Chebyshev filter circuit on the transient electrical current responses of a plasmonic nanopore sensor during abrupt voltage reversals. Those reversals are similar to ones used for single molecule capture-recapture with electrical nanopores. Our plasmonic nanopore sensor allows simultaneous recording of optical and electrical data during optical trapping of nanoparticles and their subsequent translocation through the nanopore located at the sensor’s center. The technical challenge this work aims to resolve is that the sensor’s transient response to abrupt voltage reversals is strong (near-saturation current spikes) and is also slow (return to baseline in the ms range). During this refractory period an analyte’s translocation may be obfuscated by the sensor’s transient response. Here we test the use of a Chebyshev filter as a possible means of significantly reducing the sensor’s transient response to voltage reversals so that analyte translocations are not masked by those transient responses. At the same time, we also test that electrical signatures detected during trapping of a test analyte (20 nm SiO2 nanoparticles) are not unintentionally also removed by the same filter. This work is as a first step towards developing a methodology for enabling rapid analyte recapture by our plasmonic nanopore sensor.

Plasmonic structures are widely used in modern biosensor design. various plasmonic resonant cavities could efficiently achieve a high Q-factor, improving the local field intensity to enhance photoluminescence or SERS (Surface-Enhanced Raman Scattering) of small molecules. Also, the combination between virus-like particles and plasmonic structures could significantly influence the scattering spectrum and field, which is utilized as a method for biological particle detection. In this paper, we designed one kind of gold plasmonic cavity with the shape of a split-ring. An edge gap and a bonus center bulge are introduced in the split-ring structure. Our simulation is based on Finite Difference Time Domain (FDTD) method. Polarization Indirect Microscopic Imaging (PIMI) technique is used here to detect far-field mode distribution under the resonant wavelength. The simulation results demonstrate resonant peaks in the visible spectrum at about 600 nm with a Q-factor reaches to 74. Localized hot spots are generated by an edge dipole mode and a cavity hexapole mode at resonant wavelength, which is according to dark points in the PIMI sinδ image. Also, the split-ring cavity shows a sensitivity when combined with biological particles. The scattering distribution is evidently changed as a result of energy exchange between particles and split-ring cavity, indicating a promising possibility for biosensing.

Extraordinary optical transmission (EOT) in nanohole arrays has proven to be a useful tool for biosensing applications. The enhanced light transmission observed in these structures is due to interactions between propagating surface waves and localised resonances. In this paper we present methods to both optimise the resonance peaks of nanohole array sensors and to tune their resonance wavelength. Sensor performance is enhanced by annealing. Annealing significantly increases the grain size of the gold thin-film, reducing losses and narrowing the resonance width. In addition, we show that by changing the size and arrangement of nanoholes we can control the position of their resonance peak. In doing so, we seek to improve the performance of EOT sensors for cross-reactive sensing applications.

Surface plasmon resonance (SPR) sensors are extensively used in a variety of applications. In the proposed investigation, SPR phenomena are used to detect toxic gases by employing a multilayer sensing chip. A glass prism is coated with a nano composite thin film based on different materials: gold (Au), titanium dioxide (TiO₂), and molybdenum disulfide (MoS₂). The ammonia gas is applied to the MoS₂ sensing layer of the multilayer optical sensing chip. As the ammonia gas concentration rises around the multilayer sensing structure, the resonance angle increases, indicating that the MoS2 layer refractive index has gone up significantly due to absorption of the increasing ammonia gas concentration. The measured ammonia gas concentration is based on an angle interrogation approach. The sensor performance has also been optimized for varied MoS₂ and Au layer thicknesses. This article has all the mathematical equations that are needed, and MATLAB software is used to check the results.

Food adulteration is a global concern, and developing countries are under serious threat owing to a lack of supervision and laws. Specially, milk adulterants can cause severe health risks, resulting in fatal diseases. Conventional and qualitative detection techniques are limited due to the more sophisticated way of milk adulteration and involve complexity in the processes. This paper used ultraviolet-visible-near infrared (UV-Vis-NIR) spectrophotometric measurements technique to detect the urea concentration in the milk sample. Urea concentration was taken initially at the steps of 5% and then with 10% to mix with pure milk to measure the adulteration. Results showed that the absorbance spectrum increased proportionally in the Vis and NIR regions when we increased or added the amount of urea to milk. The proposed spectrophotometry method will be a successful basis for the screening of optical wavelength to help the researcher to find out the surface plasmon resonance (SPR) phenomenon where the light and matter interaction is maximum.

Optical biosensors are compact analytical tools that have a biorecognition element combined with a transducer system, which emits an optical signal that is directly proportional to the analyte concentration. Biorecognition elements are generally biological materials such as tissues, cells, nucleic acids, antigens, antibodies, and enzymes. Optical biosensors utilize the interaction of optical fields with the analyte for optical detections. They offer some advantages over conventional analytical methods due to their fast detection abilities, high sensitivity, real time analysis, specificity, portability, and cost effectiveness. These properties capacitate optical biosensors to perform efficiently in fields like clinical diagnostics and healthcare, environmental analysis and monitoring as well as biotechnological industry. There are many configurations of optical biosensors that have been invented, which are surface plasmon resonance based (SPR), optical waveguide based, and optical resonator based. In the current study, a home-built surface plasmon resonance based optical biosensor was used to detect the presence of HIV on a gold coated surface. The results showed that the virus was detected after binding to the antibody on the surface of the gold coated slide as demonstrated by the change in transmittance intensity between the sample that had the virus and the one with no virus. These outcomes and those obtained in the previous studies in our lab will lead to the development of a multiplex optical biosensing device for the detection of HIV, HIV viral load testing as well as the detection of HIV drug resistance mutations in any given sample.

We have investigated the enhanced Raman spectra of AMR bacteria strains of E. coli using silver coated silicon nanowires SERS assay. Three different E. coli strains, E. coli CCUG17620, NCTC 13441, and A239, were detected using two different excitation laser wavelengths. We found stable and enhanced SERS spectrum using 785 nm laser as opposed to 532 nm. Future development of SERS-chip could offer a reliable platform for direct identification of the pathogen in bio-fluid samples at strains level.