Digital detection of biomarkers for low-cost, high-sensitivity diagnostics

We have demonstrated Interferometric Reflectance Imaging Sensor (IRIS) with the ability to detect single nanoscale particles. By extending single-particle IRIS to in-liquid dynamic imaging, we demonstrated real-time digital detection of individual viral pathogens as well as single molecules labeled with Au nanoparticles. With this technique we demonstrate real-time simultaneous detection of multiple targets in a single sample, as well as quantitative dynamic detection of individual biomolecular interactions for reaction kinetics measurements. This approach promises to simplify and reduce the cost of rapid diagnostics.Accepted manuscrip

Active C4 electrodes for local field potential recording applications

Extracellular neural recording, with multi-electrode arrays (MEAs), is a powerful method used to study neural function at the network level. However, in a high density array, it can be costly and time consuming to integrate the active circuit with the expensive electrodes. In this paper, we present a 4 mm × 4 mm neural recording integrated circuit (IC) chip, utilizing IBM C4 bumps as recording electrodes, which enable a seamless active chip and electrode integration. The IC chip was designed and fabricated in a 0.13 μm BiCMOS process for both in vitro and in vivo applications. It has an input-referred noise of 4.6 μV rms for the bandwidth of 10 Hz to 10 kHz and a power dissipation of 11.25 mW at 2.5 V, or 43.9 μW per input channel. This prototype is scalable for implementing larger number and higher density electrode arrays. To validate the functionality of the chip, electrical testing results and acute in vivo recordings from a rat barrel cortex are presented.R01 NS072385 - NINDS NIH HHS; 1R01 NS072385 - NINDS NIH HH

Robust visualization and discrimination of nanoparticles by interferometric imaging

Single-molecule and single-nanoparticle biosensors are a growing frontier in diagnostics. Digital biosensors are those which enumerate all specifically immobilized biomolecules or biological nanoparticles, and thereby achieve limits of detection usually beyond the reach of ensemble measurements. Here we review modern optical techniques for single nanoparticle detection and describe the single-particle interferometric reflectance imaging sensor (SP-IRIS). We present challenges associated with reliably detecting faint nanoparticles with SP-IRIS, and describe image acquisition processes and software modifications to address them. Specifically, we describe a image acquisition processing method for the discrimination and accurate counting of nanoparticles that greatly reduces both the number of false positives and false negatives. These engineering improvements are critical steps in the translation of SP-IRIS towards applications in medical diagnostics.R01 AI096159 - NIAID NIH HHSFirst author draf

High-resolution Imaging of nanoparticles in wide-field interferometric scattering microscopy

Single particle interferometric scattering microscopy has demonstrated great capability in label-free imaging of sub-wavelength dielectric nanoparticles (r<25 nm); however, it suffers from diffraction-limited resolution. Here, we demonstrate ~2-fold improvement in lateral resolution upon asymmetric illumination.Published versio

Computational nanosensing from defocus in single particle interferometric reflectance microscopy

Single particle interferometric reflectance (SPIR) microscopy has been studied as a powerful imaging platform for label-free and highly sensitive biological nanoparticle detection and characterization. SPIR's interferometric nature yields a unique 3D defocus intensity profile of the nanoparticles over a large field of view. Here, we utilize this defocus information to recover high signal-to-noise ratio nanoparticle images with a computationally and memory efficient reconstruction framework. Our direct inversion approach recovers this image from a 3D defocus intensity stack using the vectorial-optics-based forward model developed for sub-diffraction-limited dielectric nanoparticles captured on a layered substrate. We demonstrate proof-of-concept experiments on silica beads with a 50 nm nominal diameter.Accepted manuscript2021-12-0

Simultaneous evaluation of multiple microarray surface chemistries through real-time interferometric imaging.

Surface chemistry is a crucial aspect for microarray modality biosensor development. The immobilization capability of the functionalized surface is indeed a limiting factor for the final yield of the binding reaction. In this work, we were able to simultaneously compare the functionality of protein ligands that were locally immobilized on different polymers, while on the same solid support, therefore demonstrating a new way of multiplexing. Our goal was to investigate, in a single experiment, both the immobilization efficiency of a group of reactive polymers and the resulting affinity of the tethered molecules. This idea was demonstrated by spotting many reactive polymers on a Si/SiO2 chip and depositing the molecular probes on the spots immediately after. As a proof of concept, we focused on which polymers would better immobilize a model protein (α-Lactalbumin) and a peptide (LAC-1). We successfully showed that this protocol is applicable to proteins and peptides with a good efficiency. By means of real-time binding measurements performed with the interferometric reflectance imaging sensor (IRIS), local functionalization proved to be comparable to the classical flat coating solution. The final outcome highlights the multiplexing power of this method: first, it allows to characterize dozens of polymers at once. Secondly, it removes the limitation, related to coated surfaces, that only molecules with the same functional groups can be tethered to the same solid support. By applying this protocol, many types of molecules can be studied simultaneously and immobilization for each probe can be individually optimized.766466 (INDEX) - Horizon 2020 Framework Programmehttps://s3-eu-west-1.amazonaws.com/itempdf74155353254prod/8976347/Simultaneous_Evaluation_of_Multiple_Microarray_Surface_Chemistries_Through_Real-Time_Interferometric_Imaging_v1.pdfFirst author draf

Highly sensitive and label-free digital detection of whole cell E. coli with interferometric reflectance imaging

Bacterial infectious diseases are a major threat to human health. Timely and sensitive pathogenic bacteria detection is crucial in identifying the bacterial contaminations and preventing the spread of infectious diseases. Due to limitations of conventional bacteria detection techniques there have been concerted research efforts towards development of new biosensors. Biosensors offering label free, whole bacteria detection are highly desirable over those relying on label based or pathogenic molecular components detection. The major advantage is eliminating the additional time and cost required for labeling or extracting the desired bacterial components. Here, we demonstrate rapid, sensitive and label free E. coli detection utilizing interferometric reflectance imaging enhancement allowing for visualizing individual pathogens captured on the surface. Enabled by our ability to count individual bacteria on a large sensor surface, we demonstrate a limit of detection of 2.2 CFU/ml from a buffer solution with no sample preparation. To the best of our knowledge, this high level of sensitivity for whole E. coli detection is unprecedented in label free biosensing. The specificity of our biosensor is validated by comparing the response to target bacteria E. coli and non target bacteria S. aureus, K. pneumonia and P. aeruginosa. The biosensor performance in tap water also proves that its detection capability is unaffected by the sample complexity. Furthermore, our sensor platform provides high optical magnification imaging and thus validation of recorded detection events as the target bacteria based on morphological characterization. Therefore, our sensitive and label free detection method offers new perspectives for direct bacterial detection in real matrices and clinical samples.First author draf

Improved selectivity from a wavelength addressable device for wireless stimulation of neural tissue

Electrical neural stimulation with micro electrodes is a promising technique for restoring lost functions in the central nervous system as a result of injury or disease. One of the problems related to current neural stimulators is the tissue response due to the connecting wires and the presence of a rigid electrode inside soft neural tissue. We have developed a novel, optically activated, microscale photovoltaic neurostimulator based on a custom layered compound semiconductor heterostructure that is both wireless and has a comparatively small volume (&lt;0.01 mm3). Optical activation provides a wireless means of energy transfer to the neurostimulator, eliminating wires and the associated complications. This neurostimulator was shown to evoke action potentials and a functional motor response in the rat spinal cord. In this work, we extend our design to include wavelength selectivity and thus allowing independent activation of devices. As a proof of concept, we fabricated two different microscale devices with different spectral responsivities in the near-infrared region. We assessed the improved addressability of individual devices via wavelength selectivity as compared to spatial selectivity alone through on-bench optical measurements of the devices in combination with an in vivo light intensity profile in the rat cortex obtained in a previous study. We show that wavelength selectivity improves the individual addressability of the floating stimulators, thus increasing the number of devices that can be implanted in close proximity to each other. © 2014 Seymour, Freedman, Gökkavas, Özbay, Sahinand Ünlü

Introduction to the special issue of optical biosensors

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