Optical Encoding Research Articles

Multiplexed Biosensing and Bioimaging Using Lanthanide-Based Time-Gated Förster Resonance Energy Transfer.

The necessity to scrutinize more and more biological molecules and interactions both in solution and on the cellular level has led to an increasing demand for sensitive and specific multiplexed diagnostic analysis. Photoluminescence (PL) detection is ideally suited for multiplexed biosensing and bioimaging because it is rapid and sensitive and there is an almost unlimited choice of fluorophores that provide a large versatility of photophysical properties, including PL intensities, spectra, and lifetimes.The most frequently used technique to detect multiple parameters from a single sample is spectral (or color) multiplexing with different fluorophores, such as organic dyes, fluorescent proteins, quantum dots, or lanthanide nanoparticles and complexes. In conventional PL biosensing approaches, each fluorophore requires a distinct detection channel and excitation wavelength. This drawback can be overcome by Förster resonance energy transfer (FRET) from lanthanide donors to other fluorophore acceptors. The lanthanides' multiple and spectrally narrow emission bands over a broad spectral range can overlap with several different acceptors at once, thereby allowing FRET from one donor to multiple acceptors. The lanthanides' extremely long PL lifetimes provide two important features. First, time-gated (TG) detection allows for efficient suppression of background fluorescence from the biological environment or directly excited acceptors. Second, temporal multiplexing, for which the PL lifetimes are adjusted by the interaction with the FRET acceptor, can be used to determine specific biomolecules and/or their conformation via distinct PL decays. The high signal-to-background ratios, reproducible and precise ratiometric and homogeneous (washing-free) sensing formats, and higher-order multiplexing capabilities of lanthanide-based TG-FRET have resulted in significant advances in the analysis of biomolecular recognition. Applications range from fundamental analysis of biomolecular interactions and conformations to high-throughput and point-of-care in vitro diagnostics and DNA sequencing to advanced optical encoding, using both liquid and solid samples and in situ, in vitro, and in vivo detection with high sensitivity and selectivity.In this Account, we discuss recent advances in lanthanide-based TG-FRET for the development and application of advanced immunoassays, nucleic acid sensing, and fluorescence imaging. In addition to the different spectral and temporal multiplexing approaches, we highlight the importance of the careful design and combination of different biological, organic, and inorganic molecules and nanomaterials for an adjustable FRET donor-acceptor distance that determines the ultimate performance of the diagnostic assays and conformational sensors in their physiological environment. We conclude by sharing our vision on how progress in the development of new sensing concepts, material combinations, and instrumentation can further advance TG-FRET multiplexing and accelerate its translation into routine clinical practice and the investigation of challenging biological systems.

Physically-enhanced ghost encoding.

In this Letter, we propose a physically enhanced ghost encoding scheme that is realized by exploring optical channel characteristics, i.e., physically and dynamically generated scaling factors. It is found that scaling factors can be physically and dynamically generated to serve as security keys in a ghost encoding scheme, dramatically enlarging the key space and enhancing the security of optical ghost encoding schemes. To the best of our knowledge, this is the first time that dynamic scaling factors have been controlled in the optical path to realize physically enhanced ghost encoding. In addition to the illumination patterns used in optical ghost encoding schemes, the proposed method applies a variable beam attenuator and an amplitude-only spatial light modulator (SLM) to physically generate dynamic scaling factors as keys. Nonlinear variation of scaling factors is achieved in different free-space wave-propagation environments in the proposed method. A series of optical experiments are conducted to verify the feasibility and effectiveness of the proposed physically enhanced ghost encoding scheme. The proposed method could open up new research perspectives in optical ghost encoding.

A hybrid hydrogel system composed of CdTe quantum dots and photonic crystals for optical anti-counterfeiting and information encoding–decoding

A novel hybrid hydrogel system composed of CdTe QDs and SiO2 PCs was developed for optical anti-counterfeiting and information encoding–decoding.

Tailored up-conversion luminescence output of Al-modulated KYbF4: Er3+ nanocrystals for a low-temperature sensor

Tailored up-conversion luminescence output of Al-modulated KYbF4: Er3+ nanocrystals for a low-temperature sensor.

Recovery and Characterization of Orbital Angular Momentum Modes with Ghost Diffraction Holography

Orbital angular momentum (OAM) of optical vortex beams has been regarded as an independent physical dimension of light with predominant information-carrying potential. However, the presence of scattering environment and turbulent atmosphere scrambles the helical wavefront and destroys the orthogonality of modes in vortex beam propagation. Here, we propose and experimentally demonstrate a new basis for the recovery of the OAM mode using a holographic ghost diffraction scheme. The technique utilizes the speckle field generated from a rotating diffuser for optical vortex mode encoding, and the fourth-order correlation of the speckle field for the efficient recovery of the associated modes. Furthermore, we successfully demonstrate the complex-field recovery of OAM modes by the adoption of a holography scheme in combination with the ghost diffraction system. We evaluate the feasibility of the approach by simulation and followed by experimental demonstration for the recovery of various sequentially encoded OAM modes. Finally, the efficacy of the recovered modes was quantitatively analyzed by an OAM mode analysis utilizing orthogonal projection scheme.

Video encryption/compression using compressive coded rotating mirror camera

Compressive coded rotating mirror (CCRM) camera is a novel high-speed imaging system that operates under amplitude optical encoding and frame sweeping modalities in a passive imaging mode that is capable of reconstructing 1400 frames from a single shot image acquisition and achieves the highest compression ratio of 368 compared to the other compressive sensing (CS) based single-shot imaging modalities. The integrated optical encoding and compression adds a strong layer of encryption on the observed data and facilitates the integration of the CCRM camera with the imaging applications that require highly efficient data encryption and compression due to capturing highly sensitive data or limited transmission and storage capacities. CCRM uses amplitude encoding that significantly extends the key space where the probability of having the exact encoder pattern is estimated as Pleft( Aright) = 1/{10}^{122,500}, hence drastically reducing the possibility of data recovery in a brute force manner. Data reconstruction is achieved under CS based algorithms where the obtained amplitude-based pattern from optical encoder operates as the key in the recovery process. Reconstruction on the experimental as well as the synthetic data at various compression ratios demonstrate that the estimated key with less than 95% matching elements were unable to recover the data where the achieved averaged structural similarity (SSIM) of 0.25 before 95% encoder similarity and 0.85 SSIM at 100% encoder similarity demonstrates the high-sensitivity of the proposed optical encryption technique.

Designing Functionalized Polyelectrolyte Microcapsules for Cancer Treatment.

The engineering of delivery systems for drugs and contrasting labels ensuring the simultaneous imaging and treatment of malignant tumors is an important hurdle in developing new tools for cancer therapy and diagnosis. Polyelectrolyte microcapsules (MCs), formed by nanosized interpolymer complexes, represent a promising platform for the designing of multipurpose agents, functionalized with various components, including high- and low-molecular-weight substances, metal nanoparticles, and organic fluorescent dyes. Here, we have developed size-homogenous MCs with different structures (core/shell and shell types) and microbeads containing doxorubicin (DOX) as a model anticancer drug, and fluorescent semiconductor nanocrystals (quantum dots, QDs) as fluorescent nanolabels. In this study, we suggest approaches to the encapsulation of DOX at different stages of the MC synthesis and describe the optimal conditions for the optical encoding of MCs with water-soluble QDs. The results of primary characterization of the designed microcarriers, including particle analysis, the efficacy of DOX and QDs encapsulation, and the drug release kinetics are reported. The polyelectrolyte MCs developed here ensure a modified (prolonged) release of DOX, under conditions close to normal and tumor tissues; they possess a bright fluorescence that paves the way to their exploitation for the delivery of antitumor drugs and fluorescence imaging.

Multiplexed detection of bladder cancer microRNAs based on core-shell-shell magnetic quantum dot microbeads and cascade signal amplification

Bladder Cancer (BC) is the tenth most common cancer worldwide and the most malignant disease of the urinary system. The development of effective biomarkers and detection methods is of great significance for BC diagnosis and monitoring. This study demonstrated a microscopic imaging method for multiplexed detecting BC microRNAs (miRNAs) based on core-shell-shell bifunctional magnetic fluorescent beads (MFBs), with the integration of catalytic hairpin assembly (CHA) and terminal deoxynucleotidyl transferase (TdT)-mediated DNA polymerization. Assembled with quantum dots and magnetic nanoparticles, MFBs were utilized as the dual-functional carriers for optical encoding and magnetic separation. By introducing CHA-TdT cascade amplification, three encoded MFBs presented distinct changes of emissive-color, which could be decoded by the common fluorescence microscope. The strategy could reach femtomolar level for the detection of single miRNA, showing a wide linear dynamic range (6 logs). Point-mutation discrimination capability was also achieved for precise miRNA analyses. Moreover, this MFB-CHA-TdT strategy was capable of detecting BC-related miRNAs in clinical serum specimens, showing a great consistence with qRT-PCR. Overall, this work enabled multiplexed detection of miRNAs with ideal sensitivity, specificity and accuracy, which could be applied to the clinical detection and early diagnosis of BC.

Multiplexing meta-hologram with separate control of amplitude and phase.

Metasurfaces have shown their unique capabilities to manipulate the phase and/or amplitude properties of incident light at the subwavelength scale, which provides an effective approach for constructing amplitude-only, phase-only or even complexed amplitude meta-devices with high resolution. Most of meta-devices control the amplitude and/or phase of the incident light with the same polarization state; however, separately controlling of amplitude and phase of the incident light with different polarization states can provide a new degree of freedom for improving the information capacity of metasurfaces and designing multifunctional meta-devices. Herein, we combine the amplitude manipulation and geometric phase manipulation by only reconfiguring the orientation angle of the nanostructure and present a single-sized design strategy for a multiplexing meta-hologram which plays the dual roles: a continuous amplitude-only meta-device and a two-step phase-only meta-device. Two different modulation types can be readily switched merely by polarization controls. Our approach opens up the possibilities for separately and independently controlling of amplitude and phase of light to construct a multiplexing meta-hologram with a single-sized metasurface, which can contribute to the advanced research and applications in multi-folded optical anti-counterfeiting, optical information hiding and optical information encoding.

In-situ host-transition-induced upconversion luminescence modulation of ZrW2O7(OH)2·2H2O:Yb3+/Er3+ nanocrystals

Luminescence properties of upconverting nanomaterials are significantly influenced by host structures. Even though previous studies have demonstrated various modulation approaches of host structures on upconversion luminescence, in-situ host transition has been hardly realized. In this paper, we demonstrate in-situ host-transition-induced upconversion luminescence modulation based on ZrW 2 O 7 (OH) 2 ·2H 2 O:Yb 3+ /Er 3+ nanocrystals. Specifically, ZrW 2 O 7 (OH) 2 ·2H 2 O:Yb 3+ /Er 3+ could be decomposed into ZrO 2 :Yb 3+ /Er 3+ and WO 3 :Yb 3+ /Er 3+ nanocrystals due to the increased host temperature by the 980-nm-wavelength-laser-triggered photothermal heating. After the host transition, the red-to-green emission ratio of the prepared nanoparticles has been significantly increased, leading to an apparent color change in the upconversion light emission. The work is expected to open up unprecedented avenues for fluorescence anti-counterfeiting, optical encoding, and sensing applications. • Realize a convenient upconversion luminescence modulation. • Demonstrate in-situ host-transition of ZrW 2 O 7 (OH) 2 ·2H 2 O:Yb 3+ /Er 3+ nanocrystals. • Realize tunable emission colors from green to red only by laser treatment.

Optical random speckle encoding based on hybrid wavelength and phase modulation.

Optical random speckle encoding suffers from a contradiction between the generation speed and pattern amount. Spatial light modulators are commonly used for random speckle generation at relatively low speeds. Wavelength scanning combined with a scattering medium has a fast speed, while the pattern amount is limited by the optical bandwidth. To increase the performance of optical random speckle encoding, a novel, to the best of our knowledge, scheme combining wavelength and phase hybrid modulation is proposed and demonstrated. Through optical encoding in the two dimensions of wavelength and phase, the number of speckle patterns can reach one million, which is over 10,000 times that generated by only wavelength scanning. This scheme can be used in ghost imaging systems to increase the resolution of reconstructed images.

Phase Manipulation‐Based Polarization Profile Realization and Hybrid Holograms Using Geometric Metasurface

The outstanding ability of optical metasurfaces to tailor light's amplitude, phase, and polarization with a subwavelength resolution has attracted big interest. A multifunctional metasurface device is reported and experimentally demonstrated that integrates an arbitrary polarization profile for image concealment and a computer‐generated hybrid hologram. Herein, a high‐resolution image is hidden in the polarization profile of the light beam, while the holographic images are encoded in its phase profile for the reconstruction of two different types of holographic images. The designed polarization profile is realized based on the superposition of two different phase profiles for circular polarization states with opposite handedness. This method can further extend the design degree of freedom in optical metasurfaces, which may open an alternative avenue for anticounterfeiting, optical image encoding, and optical information security.

A review of optical image encryption techniques based on Cloud computing biometric and multiple image processing

Cloud Computing technology has become one of the most powerful technologies in terms of high availability, flexibility, and scalability. Besides all the widely perceived benefits of cloud computing, there is a concern that makes the use of the cloud leads to a potential risk that is security. To overcome security issues, a strong authentication mechanism is required. Biometric authentication is one of the very popular methods used for identity detection so that only an authorized person can access the system, one method to achieve this is image processing. In this paper, we review various optical image encryption techniques based on the optical Double Random Phase Encoding (DRPE) system, the oldest and most extensively investigated optical scheme. In the literature, we get an overview of digital image processing applications and data encryption schemes. The various parameter used to measure the image encryption level is discussed. The optical Double Random Phase Encoding method and its numerical simulation are then investigated. In addition to it, other optical encryptions techniques such as multiple image cryptosystem extension and different techniques are discussed that enhance the optical encryption security, which is used widely and generally appreciated. We explored the cloud framework via the biometric authentication process to authorize the legitimate user and permission checks is done by the biometric system. The level of security of the overall system increases when the authorization process is strong and faultless. The challenges faced in this area and the objectives of the research have been discussed.

Highly Stable Perovskite Quantum Dots Modified by Europium Complex for Dual-Responsive Optical Encoding.

Inorganic perovskite quantum dots (QDs) have attracted great scientific attention in the field of luminescent materials, but the application has been limited by the inferior stability that results from highly dynamic capping ligands. In this work, we use a rare-earth complex to modify perovskite QDs with ligand exchange to realize perovskite functionalization; meanwhile, the stability of perovskite QDs is greatly improved. Density functional theory calculation results show that the adsorption energy of the europium complex to QDs is higher than that with traditional ligands, which provides a thermodynamic basis for stability improvement. Furthermore, the modified QDs exhibit attractive dual-response property, including temperature and pH response ascribed to QDs and europium complexes, respectively. The superior property can be applied to multi-stimuli-responsive optical encoding, which is further capable of enhancing the security of encrypted information. This study not only affords a strategy for the synthesis of highly stable perovskites but also provides a method for the functionalization of perovskites.

Carbon dots promoted photonic crystal for optical information storage and sensing

Photonic crystals (PCs) with crack-free morphology, high-saturated structural color and sensitivity to circumstances are expanding their applications in painting, sensor, optical coding and information technology. Herein, we incorporated functionalized carbon dots (CDs) onto polystyrene@poly(methyl methacylate-co-acrylic acid) (PS@P(MMA-AA)) colloidal particles via strong covalent bonding. Thanks to the abundant hydrogen bonding groups on the CDs, as-prepared CDs/PS@P(MMA-AA) PC film exhibits highly-crystalline morphology, brilliant structural color and fluorescence characteristics. By means of microfluidics technique, CDs/PS@P(MMA-AA) PC supraballs with angle-independent structural color for optical display and encoding are also demonstrated. Moreover, the magnetism/optics dual-functional Janus and hierarchical molecular-analogue supraballs are fabricated through the triphase microfluidic device and magnetism-induced assembly, bringing about a switchable behavior of PC supraballs in external magnetic field, which are further employed as the pixel points in the panel to store and display the quick response (QR) code information. Ultimately, combined with sensitive hydrogel, the CDs/PS@P(MMA-AA) PC hydrogel is not only imparted with an intriguing mechanochromic property, but also showing the rapid response to pH value. The CDs promoted PS@P(MMA-AA) PCs with various attractive optical properties offer a potential strategy of robust PC film/supraball construction for anti-counterfeiting, optical display, sensors and antireflection coatings.

Compressive Coded Rotating Mirror Camera for High-Speed Imaging

We develop a novel compressive coded rotating mirror (CCRM) camera to capture events at high frame rates in passive mode with a compact instrument design at a fraction of the cost compared to other high-speed imaging cameras. Operation of the CCRM camera is based on amplitude optical encoding (grey scale) and a continuous frame sweep across a low-cost detector using a motorized rotating mirror system which can achieve single pixel shift between adjacent frames. Amplitude encoding and continuous frame overlapping enable the CCRM camera to achieve a high number of captured frames and high temporal resolution without making sacrifices in the spatial resolution. Two sets of dynamic scenes have been captured at up to a 120 Kfps frame rate in both monochrome and colored scales in the experimental demonstrations. The obtained heavily compressed data from the experiment are reconstructed using the optimization algorithm under the compressive sensing (CS) paradigm and the highest sequence depth of 1400 captured frames in a single exposure has been achieved with the highest compression ratio of 368 compared to other CS-based high-speed imaging technologies. Under similar conditions the CCRM camera is 700× faster than conventional rotating mirror based imaging devices and could reach a frame rate of up to 20 Gfps.

Hydrophobic fluorinated colloidal photonic crystals for heterogeneous aggregated cluster encoding and energy-saving applications

The construction of high-quality colloidal photonic crystals (CPCs) for optoelectronics, energy and biological applications, featuring the viable and effective self-driven assembly route, still remains a challenge. Herein, we demonstrate the efficient self-assembly of hydrophobic fluorine-containing poly(trifluoroethyl methacrylate) (PTFEMA) CPCs via hydrophobic force for heterogeneous aggregated cluster encoding and photoluminescence enhancement of liquid crystal display (LCD). The CPC films with periodic arranged structure self-assembled through the hydrophobic terminals (-CF3) display tunable brilliant structural color and large-area crack-free morphology. Moreover, taking advantage of PTFEMA emulsion and superparamagnetic Fe3O4 nanoparticle suspension as two discontinuous phases, Janus microbeads are fabricated by the triphase microfluidic technology, which are subsequently constructed into heterogeneous aggregated clusters that perform multiple structural color signals for the optical encoding. Eventually, the PTFEMA CPC film serves as the photoluminescence enhanced film to significantly elevate the photoluminescence (PL) intensity of CdSe@ZnS quantum dots by ca. 11 folds in an LCD device. The novel PTFEMA CPCs may offer the alternative opportunities for optical encoding towards sensing, anticounterfeiting and information storage, as well as the energy-saving optoelectronic devices.

High Color-Purity Red, Green, and Blue-Emissive Core-Shell Upconversion Nanoparticles Using Ternary Near-Infrared Quadrature Excitations.

Development of multicolor-emitting upconversion nanoparticles (UCNPs) is of significant importance for applications in optical encoding, anti-counterfeiting, display, and bioimaging. However, realizing the orthogonal three-primary color (TPC) upconversion luminescence in a single nanoparticle remains a huge challenge. Herein, we have rationally designed core-multishell-structured NaYF4 UCNPs through regulating the dopant concentration, composition of luminescent layers, and shell position and thickness, which are capable of emitting red, green, and blue luminescence with high color purity in response to ternary near-infrared quadrature excitations (1560/808/980 nm). Moreover, their high color purity is well retained with varying excitation power densities. This orthogonal TPC emissions property of such UCNPs endows them with great promise in the field of security. As a proof-of-concept, we have demonstrated the feasibility of combining such UCNPs with MnO2 nanosheets for information encryption and decryption. This work not only offers a new way to achieve TPC upconversion luminescence at a single nanoparticle level but also broadens the scope of application for security protection.

Optical encoding of luminescent carbon nanodots in confined spaces.

Stable emissive carbon nanodots were generated in zeolite crystals using near infrared photon irradiation gradually converting the occluded organic template, originally used to synthesize the zeolite crystals, into discrete luminescent species consisting of nano-sized carbogenic fluorophores, as ascertained using Raman microscopy, and steady-state and time-resolved spectroscopic techniques. Photoactivation in a confocal laser fluorescence microscope allows 3D resolved writing of luminescent carbon nanodot patterns inside zeolites providing a cost-effective and non-toxic alternative to previously reported metal-based nanoclusters confined in zeolites, and opens up opportunities in bio-labelling and sensing applications.

Optical engineering of nanoporous photonic crystals by Gaussian-Like pulse anodization

Abstract A new class of nanoporous anodic alumina photonic crystals (NAA–PCs) are optically engineered by four distinct forms of Gaussian-like pulse anodization (GLPA) – Gaussian, Lorentzian, logarithmic normal, and Laplacian. NAA–PCs produced by GLPA under current density control conditions show well-resolved, spectrally tunable photonic stopbands (PSBs), the features of which – central wavelength, full width at half maximum, intensity, and quality factor – can be precisely tuned across the UV–visible spectrum by the input Gaussian-like current density pulses. Effects of type, width, and period of Gaussian-like current density pulses on the structural and optical properties of NAA–PCs are systematically assessed. Comprehensive electrochemical, structural, and optical characterizations allow us to elucidate the interplay of input GLPA profile and structural features in determining forbidden light propagation within these NAA–PCs. Sensitivity of these PC structures toward changes in their effective medium are determined by quantifying spectral shifts in their characteristic PSB upon infiltration of their nanoporous structure with analytical solutions of alcohol mixtures with varying refractive index, from 1.362 to 1.383 RIU. It is found that, at fixed anodization period, NAA–PCs produced by Laplacian current density pulses achieve the highest sensitivity (105 ± 4 nm RIU−1) and, for a given type of GLPA, NAA–PCs produced with longer anodization period achieve higher sensitivity (123 ± 10 nm RIU−1 for NAA–PCs fabricated by Gaussian pulses with a 1400 s-period). Our advances provide exciting new opportunities for future developments of high-quality NAA–PCs with broad applicability across various photonic technologies, including optical sensing, photocatalysis, lasing, and optical encoding.