This PDF file contains the front matter associated with SPIE Proceedings Volume 12397, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

In the last decades, coupling strategies of optical microresonators have been intensively explored to develop highly sensitive and label-free miniaturized biosensors. This work presents an innovative semi-automatic assembly approach for glass microbottles on a photonic integrated circuit (PIC) with single-mode waveguides. Microbottles are extraordinary whispering- gallery-mode structures with additional axial confinement of the light along the bottle shape. A high dense spectrum of resonances varying along the bottle curvature is typically observed. To excite these resonances, the evanescent field of waveguides is used, as it provides direct evanescent interaction, integration of multiple structures and mass production. Initial coupling tests in air yielded a Q factor of 10⁴ at 1550 nm by employing an active alignment setup and a customized gripping tool. Lateral coupling tolerances of Δx = ±50 μm and Δy = ±2 μm for a bottle diameter of 180 μm were also found. An existing assembly machine including a visual system, alignment system, high precision glue dispenser and UV light was used for the identification, placement and fixation of microbottles. A highest Q factor of 10⁵ was determined after the attachment of a microbottle. Similar results were obtained with bio-chemical modified samples. A laser cutting method was also applied for reducing the fiber length of the microbottle. In this way the hybrid PIC can be compatible with microfluidics. The dedicated assembly process is a promising tool to bring optical resonators into practical use for label-free biochemical sensing but also for other applications such as quantum sensing and communication.

We report improved surface sensing capabilities of photonic crystal biosensors through the inclusion of a subwavelength dielectric feature inside the photonic crystal unit cell. Incorporation of a 50 nm silicon bar (i.e., anti-slot) spanning a traditional silicon photonic crystal unit cell increases the local energy density and consequently increases the resonance shift when molecules are captured on the sensor surface. Simulations and corroborating proof-of-concept experimental results based on a layer-by-layer polymer deposition are demonstrated. A perturbation theory approach for more computationally efficient predictions of photonic crystal biosensor performance is also reported, along with a discussion of the biosensor performance as a function of the spatial position of molecule attachment on the different sensor surfaces.

Continuous measurement of the concentrations of ethanol and its metabolites, acetaldehyde and acetic acid, in vivo is important for the alcohol research community. Most studies only measure ethanol because accurate measurement of all three compounds is challenging. Measurement inside tissue/brain is done using a microdialysis technique, followed by off-line analysis using gas chromatography (GC). To realize simultaneous measurement of ethanol and its metabolites, one can take advantage of infrared (IR) spectroscopy as a rapid and reagent-free method. Here we report a feasibility study of using IR spectroscopy to simultaneously measure ethanol, acetaldehyde and acetic acid in aqueous solution. Different concentrations in transmission mode at different optical pathlengths and using attenuated total reflectance (ATR) were measured. In vitro microdialysis was performed on the mixture of the three compounds, and the collected sample was measured using IR to demonstrate the capability of quantifying the concentrations of the three analytes simultaneously. Lastly, to overcome the limitations of the microdialysis technique, direct measurement using evanescent-field IR spectroscopy can be a potential alternative. A hydrophobic polymer coating that adsorbs ethanol and excludes water, could improve sensitivity. Sorption kinetics in polymethyl methacrylate (PMMA) and polydimethylsiloxane (PDMS) coatings on an ATR crystal were measured. Both polymers demonstrate preferential adsorption of ethanol over water.

A portable, inexpensive, and easy-to-manufacture microfluidic device is developed for the detection of SARS-CoV-2 dsDNA fragments. In this device, four reaction chambers separated by carbon fiber rods are pre-loaded with isothermal amplification and CRISPR-Cas12a reagents. The reaction is carried out by simply pulling the rods, without the need for manual pipetting. To facilitate power-free pathogen detection, the entire detection is designed to be heated with a disposable hand warmer. After the CRISPR reaction, the fluorescence signal generated by positive samples is identified by naked eye, using an inexpensive flashlight. This simple and sensitive device will serve as a new model for the next-generation viral diagnostics in either hospital or resource-limited settings.

Supramolecular optical chemosensors are useful tools in analytical chemistry for the visualization of molecular recognition information. One advantage is that they can be utilized for array systems to detect multiple analytes. However, chemosensor arrays have been evaluated mainly in the solution phase, which limits a wide range of practical applications. Thus, appropriate solid support materials such as polymer gels and paper substrates are required to broaden the scope of the application of chemosensors as on-site analytical tools. Herein, the author proposes the actual approaches for the fabrication of solid-state chemosensor arrays combined with powerful data processing techniques and portable digital recorders for real-world applications.

This article presents a lossy mode resonance (LMR) phenomenon based single mode fiber (SMF) structure for the detection of ascorbic acid (vitamin C). The fiber was etched for specified duration and then analyzed for Ascorbic acid detection. Ascorbic acid belongs to the group of drugs known as antioxidants. The body need it to boost the immune system, promote wound healing, and improve the absorption of iron from plant-based meals. The ascorbic acid test is useful for rapidly determining the levels of naturally occurring vitamin C in meals like fruit and vegetable juices etc. It can also be used to determine amount of ascorbic acid present in particular foods as a preservative or antioxidant. The proposed SMF structure will be used for the detection of ascorbic acid using graphene oxide (GO).

This study explores a novel approach to detect virus-laden droplets in the ambient air. An air-coupled photoacoustic (PA) technique is considered for this purpose. The free space PA system is developed using an air-coupled transducer with a center frequency of 350 kHz and a nanosecond pulsed laser operating at wavelength 533 nm. Water droplets containing 80 nm gold (Au) nanoparticles were aerosolized using a custom-built spraying system. The size of the droplets generated was in the range of a few hundred nanometers to 100 μm. Au nanoparticles of four concentrations (0, 8x10^-12, 16x10^-12, and 32x10-12 mol/L) were sprayed into the investigation domain interrogated by a laser beam, where the average PA signal from the droplets was 3.11±2.35, 1.28±1.26, 0.99±0.97, and 0.92±1.11 mV/mJ, respectively. The study showed, surprisingly, that water droplets without Au nanoparticles had a higher PA signal than those containing Au nanoparticles. A numerical analysis using a finite difference time domain method was used to explore the reasons for this unexpected finding. Results suggested that the undoped droplets could potentially focus the light, significantly increasing the fluence at the focus. When Au nanoparticles were present, the fluence within the droplet decreased, resulting in a lower PA signal.