The imaging of microscopic biological samples faces numerous difficulties due to their small feature sizes and low-amplitude contrast. Metalenses have shown great promise in bioimaging as they have ...access to the complete complex information, which, alongside their extremely small and compact footprint and potential to integrate multiple functionalities into a single device, allow for miniaturized microscopy with exceptional features. Here, we design and experimentally realize a dual-mode metalens integrated with a liquid crystal cell that can be electrically switched between bright-field and edge-enhanced imaging on the millisecond scale. We combine the concepts of geometric and propagation phase to design the dual-mode metalens and physically encode the required phase profiles using hydrogenated amorphous silicon for operation at visible wavelengths. The two distinct metalens phase profiles include (1) a conventional hyperbolic metalens for bright-field imaging and (2) a spiral metalens with a topological charge of +1 for edge-enhanced imaging. We demonstrate the focusing and vortex generation ability of the metalens under different states of circular polarization and prove its use for biological imaging. This work proves a method for in vivo observation and monitoring of the cell response and drug screening within a compact form factor.
Metasurfaces
A metasurface‐driven hyperspectral imaging method via multiplexed plasmonic resonance energy transfer is presented by Inhee Choi, Junsuk Rho, Luke P. Lee, and co‐workers in article ...number 2300229. The metasurface chip is designed for label‐free multifunctional quantitative biological sensing such as reactive oxygen species secretion from the living cells. The platform can significantly contribute to label‐free multifunctional molecular diagnosis, real‐time secretome monitoring, and cellular imaging.
Metasurfaces have revolutionized optical biosensing and diagnostic assays due to their sensitivity, compactness, and label-free operation. However, metasurface applications in analyzing complex ...biological systems and quantum bioscience phenomena remain scarce. In this Perspective, we discuss current developments in metasurface biosensors and propose promising future applications for probing or adopting quantum bioscience effects and improving spatial omics analysis in live cells and tissues. We discuss the capabilities of the current metasurface platforms for monitoring relevant biomarkers of viral diseases, neurodegenerative diseases, and cancers. Metasurface-empowered examination of cell morphology and secretome, virus detection, and tissue imaging can improve the accuracy of early diagnosis. Furthermore, we review device-integration approaches for point-of-care testing settings that could constitute pathways toward technology commercialization. Altogether, we provide a perspective for exploring metasurface applications in precision health and medicine.
Aluminum can sustain plasmonic resonances down into the ultraviolet (UV) range to promote surface-enhanced spectroscopy and catalysis. Despite its natural alumina passivating layer, we find here that ...under 266 nm pulsed UV illumination, aluminum can undergo a dramatic photocorrosion in water within a few tens of seconds and even at low average UV powers. This aluminum instability in water environments is a critical limitation. We show that the aluminum photocorrosion is related to the nonlinear absorption by water in the UV range leading to the production of hydroxyl radicals. Different corrosion protection approaches are tested using scavengers for reactive oxygen species and polymer layers deposited on top of the aluminum structures. Using optimized protection, we achieve a 10-fold increase in the available UV power range leading to no visible photocorrosion effects. This technique is crucial to achieve stable use of aluminum nanostructures enabling UV plasmonics in aqueous solutions.
We report a novel, dry, and clean method to directly deposit single-walled carbon nanotubes (SWCNTs) onto a desired substrate with the photophoresis phenomenon. We demonstrate the photophoresis ...method to be convenient and reproducible to deposit low-bundled nanotubes to form either non-percolating or continuous networks with controlled SWCNT density and surface distribution. Employing the structure-dependent optical features of the nanotubes, we show the correlation between the light source spectrum and the configuration of the deposited SWCNTs due to the selective light interaction with SWCNTs of certain chiralities. Thus, photophoretic deposition is a promising method for the fabrication of various advanced devices, such as electrically driven single-photon emitters or field-effect transistors from semiconducting SWCNTs with a desired electronic structure.
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•Single-walled carbon nanotubes were synthesized by the aerosol CVD method.•Novel method for the photophoretic deposition of aerosol SWCNTs was proposed.•Photophoresis can be used to deposit both individual and bundled SWCNTs.•Chirality selective photophoretic deposition was observed for the first time.
Extending plasmonics into the ultraviolet range imposes the use of aluminum to achieve the best optical performance. However, water corrosion is a major limitation for UV aluminum plasmonics, as this ...phenomenon occurs significantly faster in the presence of UV light, even at low laser powers of a few microwatts. Here, we assess the performance of nanometer-thick layers of various metal oxides deposited by atomic layer deposition (ALD) and plasma-enhanced chemical vapor deposition (PECVD) on top of aluminum nanoapertures to protect the metal against UV photocorrosion. The combination of a 5 nm Al2O3 layer covered by a 5 nm TiO2 capping provides the best resistance performance, while a single 10 nm layer of SiO2 or HfO2 is a good alternative. We also report the influence of the laser wavelength, the laser operation mode, and the pH of the solution. Appropriately choosing these conditions significantly extends the range of optical powers for which the aluminum nanostructures can be used. As an application, we demonstrate the label-free detection of streptavidin proteins with an improved signal-to-noise ratio. Our approach is also beneficial to promote the long-term stability of aluminum nanostructures. Finding the appropriate nanoscale protection against aluminum corrosion is the key to enabling the development of UV plasmonic applications in chemistry and biology.
Nanoapertures milled in metallic films called zero-mode waveguides (ZMWs) overcome the limitations of classical confocal microscopes by enabling single molecule analysis at micromolar concentrations ...with improved fluorescence brightness. While the ZMWs have found many applications in single molecule fluorescence studies, their shape has been mainly limited to be circular. Owing to the large parameter space to explore and the lack of guidelines, earlier attempts using more elaborate shapes have led to unclear conclusions whether or not the performance was improved as compared to a circular ZMW. Here, we comparatively analyze the performance of rectangular-shaped nanoapertures milled in aluminum to enhance the fluorescence emission rate of single molecules from the near infrared to the deep ultraviolet. Our new design is based on rational principles taking maximum advantage of the laser linear polarization. While the long edge of the nanorectangle is set to meet the cut-off size for the propagation of light into the nanoaperture, the short edge is reduced to 30 nm to accelerate the photodynamics while maintaining bright fluorescence rates. Our results show that both in the red and in the ultraviolet, the nanorectangles provide 50% brighter photon count rates as compared to the best performing circular ZMWs and achieve fluorescence lifetimes shorter than 300 ps. These findings can be readily used to improve the performance of ZMWs, especially for fast biomolecular dynamics, bright single-photon sources, and ultraviolet plasmonics.
Nanoapertures milled in metallic films called zero-mode waveguides (ZMWs) overcome the limitations of classical confocal microscopes by enabling single molecule analysis at micromolar concentrations with improved fluorescence brightness.
Extending plasmonics into the ultraviolet range imposes the use of aluminum to achieve the best optical performance. However, water corrosion is a major limiting issue for UV aluminum plasmonics, as ...this phenomenon occurs significantly faster in presence of UV light, even at low laser powers of a few microwatts. Here we assess the performance of nanometer-thick layers of various metal oxides deposited by atomic layer deposition (ALD) and plasma-enhanced chemical vapor deposition (PECVD) on top of aluminum nanoapertures to protect the metal against UV photocorrosion. The combination of a 5 nm Al2O3 layer covered by a 5 nm TiO2 capping provides the best resistance performance, while a single 10 nm layer of SiO2 or HfO2 is a good alternative. We also report the influence of the laser wavelength, the laser operation mode and the pH of the solution. Properly choosing these conditions significantly extends the range of optical powers for which the aluminum nanostructures can be used. As application, we demonstrate the label-free detection of streptavidin proteins with improved signal to noise ratio. Our approach is also beneficial to promote the long-term stability of the aluminum nanostructures. Finding the appropriate nanoscale protection against aluminum corrosion is the key to enable the development of UV plasmonic applications in chemistry and biology.
The poor photostability and low brightness of protein autofluorescence have been major limitations preventing the detection of label-free proteins at the single molecule level. Overcoming these ...issues, we report here a strategy to promote the photostability of proteins and use their natural tryptophan autofluorescence in the ultraviolet (UV) for fluorescence correlation spectroscopy (FCS). Combining enzymatic oxygen scavengers with antioxidants and triplet state quenchers greatly promotes the protein photostability, reduces the photobleaching probability and improves the net autofluorescence detection rate. Our results show that the underlying photochemical concepts initially derived for organic visible fluorescent dyes are quite general. Using this approach, we achieved UV fluorescence correlation spectroscopy on label-free streptavidin proteins containing only 24 tryptophan residues, 6.5x less than the current state-of-the-art. This strategy greatly extends the possibility to detect single label-free proteins with the versatility of single molecule fluorescence without requiring the presence of a potentially disturbing external fluorescent marker. It also opens new perspectives to improve the UV durability of organic devices.
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