Color-sensitive and spectrometer-free plasmonic sensor for biosensing applications

Direct detection of neuron-specific enolase using a spectrometer-free colorimetric plasmonic biosensor

Sensitive detection of a tumor marker, neuron-specific enolase (NSE), was performed by a label-free direct immunoassay based on a colorimetric plasmonic biosensor. Reflective plasmonic colors of silver nanodome arrays provided a way for a sensitive refractive index sensor based on spectrometer-free colorimetric detection. The direct detection of NSE was demonstrated by a combination of a sensitive sensor substrate and image processing. The limit of detection (LOD) for NSE was determined to be 270 pM, which is lower than the clinical threshold value of NSE used for medical diagnostics of small-cell lung cancer. Since our substrate-based colorimetric plasmonic biosensor is compatible with smartphone detection, we believe that the presented biosensor will open up a way for biosensor technology for point-of-care testing as well as mobile health applications.

A novel intelligent chromo capsule endoscope for the diagnosis of neoplastic lesions in the gastrointestinal tract

Background

Chromoendoscopy has not been fully integrated into capsule endoscopy. This study aimded to develop and validate a novel intelligent chromo capsule endoscope (ICCE).

Methods

The ICCE has two modes: a white-light imaging (WLI) mode and an intelligent chromo imaging (ICI) mode. The performance of the ICCE in observing colors, animal tissues, and early gastrointestinal (GI) neoplastic lesions in humans was evaluated. Images captured by the ICCE were analysed using variance of Laplacian (VoL) values or image contrast evaluation.

Results

For color observation, conventional narrow-band imaging endoscopes and the ICI mode of the ICCE have similar spectral distributions. Compared with the WLI mode, the ICI mode had significantly higher VoL values for animal tissues (2.154 ± 1.044 vs 3.800 ± 1.491, P = 0.003), gastric precancerous lesions and early gastric cancers (2.242 ± 0.162 vs 6.642 ± 0.919, P < 0.001), and colon tumors (3.896 ± 1.430 vs 11.882 ± 7.663, P < 0.001), and significantly higher contrast for differentiating tumor and non-tumor areas (0.069 ± 0.046 vs 0.144 ± 0.076, P = 0.005). More importantly, the sensitivity, specificity, and accuracy of the ICI mode for early GI tumors were 95.83%, 91.67%, and 94.64%, respectively, which were significantly higher than the values of the WLI mode (78.33% [P < 0.001], 77.08% [P = 0.01], and 77.98% [P < 0.001], respectively).

Conclusions

We successfully integrated ICI into the capsule endoscope. The ICCE is an innovative and useful tool for differential diagnosis based on contrast-enhanced images and thus has great potential as a superior diagnostic tool for early GI tumor detection.

An Improved Automated High-Throughput Efficient Microplate Reader for Rapid Colorimetric Biosensing

A high-throughput instrument to measure the full spectral properties of biochemical agents is necessary for fast screening in fields such as medical tests, environmental monitoring, and food analysis. However, this need has currently not been fully met by the commercial microplate reader (CMR). In this study, we have developed an automated high-throughput efficient microplate reader (AHTEMR) platform by combining a spectrometer and high-precision ball screw two-dimensional motion slide together, for high-throughput and full-spectrum-required biochemical assays. A two-dimensional slide working on a ball screw was driven by a stepper motor with a custom-designed master control circuit and used as a motion system of the AHTEMR platform to achieve precise positioning and fast movement of the microplate during measurements. A compact spectrometer was coupled with an in-house designed optical pathway system and used to achieve rapid capture of the full spectral properties of biochemical agents. In a performance test, the AHTEMR platform successfully measured the full spectral absorbance of bovine serum albumin (BSA) and glucose solution in multiple wells of the microplate within several minutes and presented the real-time full spectral absorbance of BSA and glucose solution. Compared with the CMR, the AHTEMR is 79 times faster in full-spectrum measurements and 2.38 times more sensitive at the optimal wavelength of 562 nm. The rapid measurement also demonstrated the great capacity of the AHTEMR platform for screening out the best colorimetric wavelengths for tests of BSA and glucose development, which will provide a promising approach to achieving high-throughput and full-spectrum-required biochemical assays.

A multichannel color filter with the functions of optical sensor and switch

This paper reports a multichannel color filter with the functions of optical sensor and switch. The proposed structure comprises a metal-insulator-metal (MIM) bus waveguide side-couples to six circular cavities with different sizes for filtering ultra-violet and visible lights into individual colors in the wavelength range of 350-700 nm. We used the finite element method to analyze the electromagnetic field distributions and transmittance properties by varying the structural parameters in detail. The designed plasmonic filter takes advantage of filtering out different colors since the light-matter resonance and interference between the surface plasmon polaritons (SPPs) modes within the six cavities. Results show that the designed structure can preferentially select the desired colors and confine the SPPS modes in one of the cavities. This designed structure can filter eleven color channels with a small full width at half maximum (FWHM) ~ 2 nm. Furthermore, the maximum values of sensitivity, figure of merit, quality factor, dipping strength, and extinction ratio can achieve of 700 nm/RIU, 350 1/RIU, 349.0, 65.04%, and 174.50 dB, respectively, revealing the excellent functions of sensor performance and optical switch, and offering a chance for designing a beneficial nanophotonic device.

Scalable and High-Throughput Top-Down Manufacturing of Optical Metasurfaces

Metasurfaces have shown promising potential to miniaturize existing bulk optical components thanks to their extraordinary optical properties and ultra-thin, small, and lightweight footprints. However, the absence of proper manufacturing methods has been one of the main obstacles preventing the practical application of metasurfaces and commercialization. Although a variety of fabrication techniques have been used to produce optical metasurfaces, there are still no universal scalable and high-throughput manufacturing methods that meet the criteria for large-scale metasurfaces for device/product-level applications. The fundamentals and recent progress of the large area and high-throughput manufacturing methods are discussed with practical device applications. We systematically classify various top-down scalable patterning techniques for optical metasurfaces: firstly, optical and printing methods are categorized and then their conventional and unconventional (emerging/new) techniques are discussed in detail, respectively. In the end of each section, we also introduce the recent developments of metasurfaces realized by the corresponding fabrication methods.

Plasmonic Metasensors Based on 2D Hybrid Atomically Thin Perovskite Nanomaterials

In this work, we have designed highly sensitive plasmonic metasensors based on atomically thin perovskite nanomaterials with a detection limit up to 10⁻¹⁰ refractive index units (RIU) for the target sample solutions. More importantly, we have improved phase singularity detection with the Goos–Hänchen (GH) effect. The GH shift is known to be closely related to optical phase signal changes; it is much more sensitive and sharp than the phase signal in the plasmonic condition, while the experimental measurement setup is much more compact than that of the commonly used interferometer scheme to exact the phase signals. Here, we have demonstrated that plasmonic sensitivity can reach a record-high value of 1.2862 × 10⁹ µm/RIU with the optimum configurations for the plasmonic metasensors. The phase singularity-induced GH shift is more than three orders of magnitude larger than those achievable in other metamaterial schemes, including Ag/TiO₂ hyperbolic multilayer metamaterials (HMMs), metal–insulator–metal (MIM) multilayer waveguides with plasmon-induced transparency (PIT), and metasurface devices with a large phase gradient. GH sensitivity has been improved by more than 10⁶ times with the atomically thin perovskite metasurfaces (1.2862 × 10⁹ µm/RIU) than those without (918.9167 µm/RIU). The atomically thin perovskite nanomaterials with high absorption rates enable precise tuning of the depth of the plasmonic resonance dip. As such, one can optimize the structure to reach near zero-reflection at the resonance angle and the associated sharp phase singularity, which leads to a strongly enhanced GH lateral shift at the sensor interface. By integrating the 2D perovskite nanolayer into a metasurface structure, a strong localized electric field enhancement can be realized and GH sensitivity was further improved to 1.5458 × 10⁹ µm/RIU. We believe that this enhanced electric field together with the significantly improved GH shift would enable single molecular or even submolecular detection for hard-to-identify chemical and biological markers, including single nucleotide mismatch in the DNA sequence, toxic heavy metal ions, and tumor necrosis factor-α (TNFα).

Extension of the Measurable Wavelength Range for a Near-Infrared Spectrometer Using a Plasmonic Au Grating on a Si Substrate

In this paper, we proposed near-infrared spectroscopy based on a Si photodetector equipped with a gold grating and extended the measurable wavelength range to cover 1200-1600 nm by improving a spectrum derivation procedure. In the spectrum derivation, photocurrent data during alteration of the incidence angle of the measured light were converted using a responsivity matrix R, which determines the spectroscopic characteristics of the photodetector device. A generalized inverse matrix of R was used to obtain the spectrum and to fit a situation where multiple surface plasmon resonance (SPR) peaks appeared in the scanning range. When light composed of two wavelengths, 1250 nm and 1450 nm, was irradiated, the two wavelengths were distinctively discriminated using the improved method.