Microcavity- and Microlaser-Based Optical Barcoding: A Review of Encoding Techniques and Applications

Functional oligo- and polypeptide assemblies for photochemical, optical and electronic applications

The primary and secondary structures of peptides are useful as scaffolds to sequentially arrange functional groups of molecules. In this review, we review self-assembled functional peptides, whereby peptides with appropriate amino acid sequences can assemble using functional groups on their side chains. First, we apply our design strategies for the synthesis of peptide-based materials with sequenced side chains with polar moieties, organic dyes and metal complexes. The synthetic oligopeptides thus obtained exhibit inherent photoinduced charge separation and electrochemical redox activities, as well as responses to bio-sequences. Next, catalytic and photocatalytic oxidation reduction reactions and hydrogen evolution reactions are shown by utilizing the peptides with separated functionalities on both sides of β-sheets by hybridizing with electro- and photoactive graphene oxide and metal nanoparticles. Finally, the self-assembled natural proteins that form micrometre-scale spherical geometry and fibres are utilized for optical and electronic applications. The silk fibroin forms well-defined microspheres with smooth surface morphology, leading to properties suitable for use in optical resonators, which can sense external humidity because of the hygroscopic nature of silk fibroin. Dragline silk fibres can act as optical waveguides that can perform intermediate natural polymer-based optical logic operations. These functional peptides are utilizable for various applications in catalysis, optics and electronics.

Advancements and Perspectives in Optical Biosensors

Optical biosensors exhibit immense potential, offering extraordinary possibilities for biosensing due to their high sensitivity, reusability, and ultrafast sensing capabilities. This review provides a concise overview of optical biosensors, encompassing various platforms, operational mechanisms, and underlying physics, and it summarizes recent advancements in the field. Special attention is given to plasmonic biosensors and metasurface-based biosensors, emphasizing their significant performance in bioassays and, thus, their increasing attraction in biosensing research, positioning them as excellent candidates for lab-on-chip and point-of-care devices. For plasmonic biosensors, we emphasize surface plasmon resonance (SPR) and its subcategories, along with localized surface plasmon resonance (LSPR) devices and surface enhance Raman spectroscopy (SERS), highlighting their ability to perform diverse bioassays. Additionally, we discuss recently emerged metasurface-based biosensors. Toward the conclusion of this review, we address current challenges, opportunities, and prospects in optical biosensing. Considering the advancements and advantages presented by optical biosensors, it is foreseeable that they will become a robust and widespread platform for early disease diagnostics.

Continuous-Wave Pumped Monolayer WS2 Lasing for Photonic Barcoding

Micro/nano photonic barcoding has emerged as a promising technology for information security and anti-counterfeiting applications owing to its high security and robust tamper resistance. However, the practical application of conventional micro/nano photonic barcodes is constrained by limitations in encoding capacity and identification verification (e.g., broad emission bandwidth and the expense of pulsed lasers). Herein, we propose high-capacity photonic barcode labels by leveraging continuous-wave (CW) pumped monolayer tungsten disulfide (WS2) lasing. Large-area, high-quality monolayer WS2 films were grown via a vapor deposition method and coupled with external cavities to construct optically pumped microlasers, thus achieving an excellent CW-pumped lasing with a narrow linewidth (~0.39 nm) and a low threshold (~400 W cm-2) at room temperature. Each pixel within the photonic barcode labels consists of closely packed WS2 microlasers of varying sizes, demonstrating high-density and nonuniform multiple-mode lasing signals that facilitate barcode encoding. Notably, CW operation and narrow-linewidth lasing emission could significantly simplify detection. As proof of concept, a 20-pixel label exhibits a high encoding capacity (2.35 × 10108). This work may promote the advancement of two-dimensional materials micro/nanolasers and offer a promising platform for information encoding and security applications.

Intracellular biocompatible hexagonal boron nitride quantum emitters as single-photon sources and barcodes

Color centers in hexagonal boron nitride (hBN) have been emerging as a multifunctional platform for various optical applications including quantum information processing, quantum computing and imaging. Simultaneously, due to its biocompatibility and biodegradability hBN is a promising material for biomedical applications. In this work, we demonstrate single-photon emission from hBN color centers embedded inside live cells and their application to cellular barcoding. The generation and internalization of multiple color centers into cells was performed via simple and scalable procedure while keeping the cells unharmed. The emission from live cells was observed as multiple diffraction-limited spots, which exhibited excellent single-photon characteristics with high single-photon purity of 0.1 and superb emission stability without photobleaching or spectral shifts over several hours. Due to different emission wavelengths and peak widths of the color centers, they were employed as barcodes. We term them Quantum Photonic Barcodes (QPBs). Each QPB can exist in one out of 470 possible distinguishable states and a combination of a few QPBs per cell can be used to uniquely tag virtually an unlimited number of cells. The barcodes developed here offer some excellent properties, including ease of production by a single-step procedure, biocompatibility and biodegradability, emission stability, no photobleaching, small size and a huge number of unique barcodes. This work provides a basis for the use of hBN color centers for robust barcoding of cells and due to the single photon emission, presented concepts could in future be extended to quantum-limited sensing and super-resolution imaging.

Hidden imaging in thin polymer films with embedded fluorescent peptide nanodots

Fluorescent (FL) encrypting nanostructures, such as quantum dots, carbon dots, organic dyes, lanthanide nanocrystals, DNA, and more, are effective tools for advanced applications in high-resolution hidden imaging. These applications include tracking, labeling, security printing, and anti-counterfeiting drug technology. In this work, what we believe to be a new FL encoding nanostructures has been proposed, which consists of recently discovered nanometer-scale peptide dots. When refolded into a beta-sheet peptide secondary structure, these biocompatible nanoparticles exhibit a strong and tunable FL effect. The biophotonic FL covers the entire visible spectrum, making the peptide dots next-generation nanoscale light sources with a quantum yield of 30%. Our studies demonstrate that these FL bio-nanodots also exhibit a significant irreversible photo-bleaching effect associated with the light-induced destruction of noncovalent intermolecular hydrogen bonds of the peptide dots' highly stable beta-sheet secondary structure. We present what we believe is a new approach for achieving high-resolution long-term optical memory by tailoring various hidden images in the developed thin polyvinyl alcohol (PVA) polymer films with an embedded dense array of FL peptide nanodots. The technology enables recording photo-bleached patterns, barcodes, and high-resolution images.

Poly(lactic acid) stereocomplex microspheres as thermally tolerant optical resonators

Thermally tolerant polymer optical resonators are fabricated from a stereocomplex of poly(L-lactic acid) and poly(D-lactic acid) through the oil-in-water miniemulsion method. The thermal stability of the microspheres of the stereocomplex poly(lactic acid) (SC-PLA) is superior to that of the homochiral poly(lactic acid) (HC-PLA). As a result of the high thermal stability, the optical resonator properties of the SC-PLA microspheres are preserved at an elevated temperature of up to 230 °C, which is 70 °C higher than that of microspheres formed from HC-PLA.

Spatially Resolved Organic Whispering-Gallery-Mode Hetero-Microrings for High-Security Photonic Barcodes

Whispering-gallery-mode (WGM) microcavities featuring distinguishable sharp peaks in a broadband exhibit enormous advantages in the field of miniaturized photonic barcodes. However, such kind of barcodes developed hitherto are primarily based on microcavities wherein multiple gain medias were blended into a single matrix, thus resulting in the limited and indistinguishable coding elements. Here, a surface tension assisted heterogeneous assembly strategy is proposed to construct the spatially resolved WGM hetero-microrings with multiple spatial colors along its circular direction. Through precisely regulating the charge-transfer (CT) strength, full-color microrings covering the entire visible range were effectively acquired, which exhibit a series of sharp and recognizable peaks and allow for the effective construction of high-quality photonic barcodes. Notably, the spatially resolved WGM hetero-microrings with multiple coding elements were finally acquired through heterogeneous nucleation and growth controlled by the directional diffusion between the hetero-emulsion droplets, thus remarkably promoting the security strength and coding capacity of the barcodes. The results would be useful to fabricate new types of organic hierarchical hybrid WGM heterostructures for optical information recording and security labels.