SignificanceAdvances in label-free imaging have impacted many areas of biological and biomedical imaging ranging from cell biology and cancer to pathology and neuroscience. Despite the great progress and advantages of these methods, it is clear that to realize their full potential, validation by extrinsic labels and probes is critically needed.AimThis perspective calls for developing and applying innovative labels and probes to validate both existing and emerging label-free imaging methods.ApproachMajor representative types of label-free imaging methods are briefly presented discussing their advantages and differing contrasts. Their biological applications are also reviewed with a focus on how validation of label-free methods with carefully developed labeling approaches will greatly aid in further intrinsic contrast imaging adoption and likely lead to more sophisticated image-based biomarkers and a better understanding of the underlying signals.ConclusionsExpanded efforts in extrinsic label validation will significantly push forward the utilization and adoption of label-free methods both in basic research and clinical models.
Mid-infrared (MIR) vibrational spectroscopy is a non-invasive and label-free analytical method; thus, it has become an essential technique for examining biological samples and tissues. Research has shown that this method, MIR spectral imaging (MIRSI), can identify various diseases with implications for enhanced biomedical tissue diagnostics. Nonetheless, the diverse chemical makeup of tissues and their spatial heterogeneity, combined with the innately weak interaction between infrared light and biological molecules, limit the efficacy of conventional MIRSI. We introduce a new chemical tissue analysis method that uses plasmonic metasurfaces enabling the detailed molecular mapping of tissue sections. The proposed surface-enhanced chemical imaging method using plasmonic metasurfaces has excellent potential for translational biomedical research and clinical histopathology.
SignificanceLabel-free multimodal imaging methods that can provide complementary structural and chemical information from the same sample are critical for comprehensive tissue analyses. These methods are specifically needed to study the complex tumor-microenvironment where fibrillar collagen’s architectural changes are associated with cancer progression. To address this need, we present a multimodal computational imaging method where mid-infrared spectral imaging (MIRSI) is employed with second harmonic generation (SHG) microscopy to identify fibrillar collagen in biological tissues.AimTo demonstrate a multimodal approach where a morphology-specific contrast mechanism guides an MIRSI method to detect fibrillar collagen based on its chemical signatures.ApproachWe trained a supervised machine learning (ML) model using SHG images as ground truth collagen labels to classify fibrillar collagen in biological tissues based on their mid-infrared hyperspectral images. Five human pancreatic tissue samples (sizes are in the order of millimeters) were imaged by both MIRSI and SHG microscopes. In total, 2.8 million MIRSI spectra were used to train a random forest (RF) model. The other 68 million spectra were used to validate the collagen images generated by the RF-MIRSI model in terms of collagen segmentation, orientation, and alignment.ResultsCompared with the SHG ground truth, the generated RF-MIRSI collagen images achieved a high average boundary F-score (0.8 at 4-pixel thresholds) in the collagen distribution, high correlation (Pearson’s R 0.82) in the collagen orientation, and similarly high correlation (Pearson’s R 0.66) in the collagen alignment.ConclusionsWe showed the potential of ML-aided label-free mid-infrared hyperspectral imaging for collagen fiber and tumor microenvironment analysis in tumor pathology samples.
Label-free and nondestructive mid-infrared (MIR) vibrational hyperspectral imaging has gained significance as a valuable analytical tool for analyzing biomedical tissue samples. However, the complex chemical composition and heterogeneous nature of tissue specimens along with the weak interaction of infrared light with biomolecules, pose limitations on the analytical performance of traditional MIR chemical imaging. In this talk, I will introduce an advanced MIR spectrochemical tissue imaging technique that utilizes plasmonic metasurfaces to enable the capture of quantitative molecular maps of large-area murine brain tissue sections. The proposed surface-enhanced chemical imaging method using plasmonic metasurfaces has great potential for translational biomedical research and diagnostic clinical histopathology.
Surveillance of population immunity against infectious diseases is critical for pandemic management and risk assessment of future outbreaks. However, current serological tests fall short in accurately identifying immunity profiles from diverse populations. We present a label-free, rapid, multiplexed, and variant-sensitive nanoplasmonic biosensor to quantify antibodies against multiple SARS-CoV-2 antigens from small human blood samples. We combined a machine learning model with antigen-specific antibody patterns measured from four different cohorts with known COVID-19 immunity. Subsequently, we tested our model on 100 blind human samples and determine that our findings are consistent with public epidemiological data showing that our nanobiosensor can help monitor population health during a pandemic.
Label-free and nondestructive mid-infrared (MIR) vibrational hyperspectral imaging has emerged as a valuable ex-vivo tool for biomedical tissue analysis. However, due to the chemically complex and heterogeneous composition of tissue specimens, the analytical performance of conventional MIR spectral histopathology is limited. We introduce an innovative MIR spectrochemical tissue imaging modality that uses plasmonic metasurfaces to support strong surface-localized electromagnetic fields, enabling the capture of quantitative molecular maps of large-area brain tissue sections. Our surface-enhanced chemical imaging method has broad potential applications in both translational biomedical research and diagnostic clinical histopathology.
KEYWORDS: Biosensors, Nanoplasmonics, Plasmonics, Digital imaging, Proteins, Biological research, Biosensing, Nanoparticles, Light-matter interactions, Medical research
We present a nanoparticle (NP) enhanced imaging-based plasmonic biosensing technique using gold nanohole arrays (Au-NHAs) that enables highly sensitive protein detection with single analyte resolution in a one-step sandwich immunoassay. By digital quantification of individual Au-NP bound molecules on large area plasmonic surface, the portable biosensor enables rapid and robust detection of disease biomarkers from patient serum in hospital settings. Using mass-scalable deep-UV lithography (DUVL) sensor fabrication and simple LED based imaging set-up in a microarray format, our novel technology provides a powerful tool for clinical biomarker detection in a highly multiplexed manner.
We propose a disruptive point-of-care (PoC) imaging platform based on lens-free interference phase-contrast imaging for rapid detection of biomarker such as for sepsis and potentially other diseases (e.g. cancer). It enables simultaneous analysis of potentially up to 10,000 functionalized microarray spots with different biomarkers with fast time-to-results (few minutes) and by consuming a small sample volume (~10 μL). The high sensitivity allows direct measurements of the biomarker binding without the use of fluorescent labels (e.g. ELISA) or microbial culture methods. In addition, adhoc plasmonic nano-structuring is utilized to significantly improve the sensitivity for biomarker detection (optical path difference ~Å) to concentration levels relevant for disease diagnosis.
The proposed technology incorporates a portable and low-cost lens-free imaging reader made of consumer electronic components, plasmonic microarrays with distinct functionalization, and user-friendly software based on a novel phaseshifting interferometry method for topography and refractive index analysis. Due to its compactness and cost-efficiency, we foresee a great potential for PoC applications, especially for the rapid detection of infectious diseases or lifethreatening conditions, e.g. sepsis, but also for clinical trials of drugs and food control.
Cell signaling activities play a critical role in physiological and disease processes. The analysis of the tumor microenvironment or the immune system activation is nowadays providing valuable insights towards disease understanding and novel therapies development. Due to the various dynamic profiles, it is essential to implement a continuous monitoring methodology for accurate analysis. The current fluorescent and colorimetric approaches hinder such applications due to their multiple time-consuming steps, molecular labeling, and the ‘snapshot’ endpoint readouts. Photonics technology, and especially nanoplasmonic biosensors offer a unique opportunity to implement lab-on-a-chip systems that provide highly sensitive and label-free analysis of cell signaling events in real time. Here, we will present a microfluidics-integrated nanoplasmonic biosensor for long-term and real-time monitoring of cell secretion activity. The biosensor consists of a gold nanohole array supporting extraordinary optical transmission (EOT), which has been optimized to enable ultra-sensitive and high-throughput biomolecular detection. The nanobiosensor is integrated with a specifically designed microfluidic system that provides well-controlled cell culture conditions for long-term monitoring. We achieved an outstanding sensitivity for the detection of vascular endothelial growth factor (VEGF) directly secreted from microfluidic-cultured cancer cells. We demonstrated real-time monitoring for over 10 hours, preserving good cell viability. The multiplexing capability of our nanobiosensor could enable simultaneous analysis of different cell types and molecules-of-interest. Thus, our innovative approach of probing live cells can be a powerful tool to evaluate cellular activities for diagnostics and novel therapy development.
The implementation of multiplexed point-of-care biosensors is a top priority to address the current epidemic problems originated by widespread pathogenic infections, like those caused by viruses or bacteria. A rapid and accurate detection, identification, and quantification of the infectious pathogens is essential not only to facilitate a prompt treatment but also to prevent onward transmission, reduce economic expenses, and significantly promote healthcare in resource-constrained environments. We have developed a nanoplasmonic biosensor based on nanohole arrays for fast and highly sensitive analysis in a simple and direct configuration. Our microarray is integrated into a microfluidic system to allow for highthroughput detection of multiple targets in a few minutes, without the need of sample pretreatment or amplification steps. Previously, we demonstrated the utility of the biosensor for the detection of hazardous live viruses, such as the Ebola or Vaccinia viruses, measured directly in biological media. Most recently we proved the truly multiplexing capability of our plasmonic microarray with the simultaneous identification and quantification of Chlamydia trachomatis and Neisseria gonorrhoeae in urine samples. We are able to detect and distinguish the two different bacteria with detection limits in the range of 102 -103 bacteria/mL. With recent advances in plasmonics, optimized surface chemistry, and microfluidics integration, our biosensors could provide a non-invasive and rapid diagnosis at the point of care, especially when we combine the detection on a compact and low-cost optical reader.
Our goal is to develop a rectifying antenna (rectenna) applicable to solar spectrum energy harvesting. In particular, we
aim to demonstrate viable techniques for converting portion of the solar spectrum not efficiently converted to electric
power by current photovoltaic approaches. Novel design guidelines are suggested for rectifying antenna coupled
tunneling diodes. We propose a new geometric field enhancement scheme in antenna coupled tunneling diodes that uses
surface plasmon resonances. For this purpose, we have successfully implemented a planar tunneling diode with
polysilion/SiO2/polysilcon structure. An antenna coupled asymmetric tunneling diode is developed with a pointed
triangle electrode for geometric field enhancement. The geometrically asymmetric tunneling diode shows a unique
asymmetric tunneling current versus voltage characteristic. Through comparison with crossover tunneling diodes, we
verified that the current asymmetry is not from the work function difference between the two electrodes. Results of RF
rectification tests using the asymmetric diode demonstrate that our approach is practical for energy harvesting
application. Furthermore, we describe how surface plasmons can enhance the electric field across the tunnel junction,
lowering the effective "turn-on" voltage of the diode, further improving rectification efficiency.
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