Optical Signal Response Research Articles

Engineering modular and tunable single-molecule sensors by decoupling sensing from signal output.

Biosensors play key roles in medical research and diagnostics. However, the development of biosensors for new biomolecular targets of interest often involves tedious optimization steps to ensure a high signal response at the analyte concentration of interest. Here we show a modular nanosensor platform that facilitates these steps by offering ways to decouple and independently tune the signal output as well as the response window. Our approach utilizes a dynamic DNA origami nanostructure to engineer a high optical signal response based on fluorescence resonance energy transfer. We demonstrate mechanisms to tune the sensor's response window, specificity and cooperativity as well as highlight the modularity of the proposed platform by extending it to different biomolecular targets including more complex sensing schemes. This versatile nanosensor platform offers a promising starting point for the rapid development of biosensors with tailored properties.

Single ZnO Nanowire for Electrical and Optical NO2 Gas Sensing: Origin of Reversible and Irreversible Gas Effects Investigated by Photoluminescence Spectroscopy.

In this work, the gas sensing properties of a single ZnO nanowire (NW) are investigated, simultaneously in terms of photoluminescence (PL) and photocurrent (PC) response to NO2 gas, with the purpose of giving new insights on the gas sensing mechanism of a single 1D ZnO nanostructure. A single ZnO NW sensing device was fabricated, characterized, and compared with a sample made of bundles of ZnO NWs. UV near-band-edge PL emission spectroscopy was carried out at room temperature and by lowering the temperature down to 77 K, which allows detection of resolved PL peaks related to different excitonic transition regions. Surface effects were observed in PL maps, considering different nano and microstructures. Electrical and optical measurements were acquired at the same time during the NO2 gas exposure, allowing for the comparison of PL and PC response times and signal recovery. During NO2 gas desorption, irreversible behavior in the surface-related and donor-acceptor pair (DAP) regions is interpreted as the effect of an initial transient when electronic transfer from the gas molecules to the bulk occurs through the ZnO NW surface which acts as a channel. To the best of our knowledge, this is the first work which investigates the simultaneous PL optical and PC electrical response signals of a single ZnO NW to gas exposure.

Magneto-optical characterization of TCO films using standard and enhanced configurations

Thin film samples like transparent conducting oxides (TCO) are typically investigated using measurements like Hall Effect and 4-point probe measurements. We use a sensitive AC Faraday rotation (FR) setup to study thin film samples for which a magneto-optic response is challenging to characterize. The experimental setup employs a stabilized He-Ne laser (633 nm) along with an AC magnetic field that enables lock-in detection. We investigate a series of TCO samples that are deposited on a glass substrate. The TCO samples include the more widely used Indium Tin Oxide (ITO) and the relatively newer Fluorine doped Tin Oxide films, usually referred to as FTO. These films have a magneto-optic response due to the presence of free carrier concentration and therefore measurement of this response (Verdet constant) could allow one to determine the carrier concentration of these films. Given that magneto optic responses like FR depend on the length of the sample length traveled by light, these sub-micron films pose considerable challenges in trying to extract the FR response of the film from that of the much thicker glass substrate. Furthermore, we present details of the design and FR characterization of samples using a Michelson interferometer-based measurement setup which enhances the Faraday rotation and affords a new means of studying harmonic peaks of the recorded optical signal in response to a sinusoidally-varying applied magnetic field. We compare some early results from this setup to the typical “single-pass” setup to highlight the difference in the recorded signals from the two setups. To showcase the advantages of the proposed measurements, we also include some early results from a very different type of sample, namely superparamagnetic nanoparticles (SNPs).

Fluorescence-plane polarization for the real-time monitoring of transferase migration in living cells.

Transferases are enzymes that exhibit multisite migration characteristics. Significantly, enzyme activity undergoes changes during this migration process, which inevitably impacts the physiological function of living organisms and can even lead to related malignant diseases. However, research in this field has been severely hindered by the lack of tools for the simultaneous and differential monitoring of site-specific transferase activity. Herein, we propose a novel strategy that integrates a fluorescence signal response with high sensitivity and an optical rotation signal response with superior spatial resolution. To validate the feasibility of this strategy, transferase γ-glutamyltransferase (GGT) was used as a model system to develop dual-mode chiral probes ACx-GGTB (AC17-GGTB and AC15-GGTB) using chiral amino acids as specific bifunctional recognition groups. The probes undergo structural changes under GGT, resulting in the release of bifunctional recognition groups (chiral amino acids) and simultaneously generate fluorescence signals and optical rotation signals. This dual-mode output exhibits high sensitivity and facilitates differentiation of sites. Furthermore, it enables simultaneous and differential detection of GGT activity at different sites during migration. We anticipate that probes developed based on this strategy will facilitate imaging-based monitoring of the activity for other transferases, thus providing an imaging platform suitable for the real-time tracking of transferase activity changes during migration.

Quantum dynamics simulations of the 2D spectroscopy for exciton polaritons.

We develop an accurate and numerically efficient non-adiabatic path-integral approach to simulate the non-linear spectroscopy of exciton-polariton systems. This approach is based on the partial linearized density matrix approach to model the exciton dynamics with explicit propagation of the phonon bath environment, combined with a stochastic Lindblad dynamics approach to model the cavity loss dynamics. Through simulating both linear and polariton two-dimensional electronic spectra, we systematically investigate how light-matter coupling strength and cavity loss rate influence the optical response signal. Our results confirm the polaron decoupling effect, which is the reduced exciton-phonon coupling among polariton states due to the strong light-matter interactions. We further demonstrate that the polariton coherence time can be significantly prolonged compared to the electronic coherence outside the cavity.

Enhanced Multiwavelength Response of Flexible Synaptic Transistors for Human Sunburned Skin Simulation and Neuromorphic Computation.

In biological species, optogenetics and bioimaging work together to regulate the function of neurons. Similarly, the light-controlled artificial synaptic system not only enhances computational speed but also simulates complex synaptic functions. However, reported synaptic properties are mainly limited to mimicking simple biological functions and single-wavelength responses. Therefore, the development of flexible synaptic devices with multiwavelength optical signal response and multifunctional simulation remains a challenge. Here, flexible organic light-stimulated synaptic transistors (LSSTs) enabled by alumina oxide (AlOX ), with a simple fabrication process, are reported. By embedding AlOX nanoparticles, the excitons separation efficiency is improved, allowing for multiple wavelength responses. Optimized LSSTs can respond to multiple optical and electrical signals in a highly synaptic manner. Multiwavelength optical synaptic plasticity, electrical synaptic plasticity, sunburned skin simulation, learning efficiency model controlled by photoelectric cooperative stimulation, neural network computing, "deer" picture learning and memory functions are successfully proposed, which promote the development for future artificial intelligent systems. Furthermore, as prepared flexible transistors exhibit mechanical flexibility with bending radius down to 2.5mm and improved photosynaptic plasticity, which facilitating development of neuromorphic computing and multifunction integration systems at the device-level.

Label-Free Direct Detection of Cylindrospermopsin via Graphene-Enhanced Surface Plasmon Resonance Aptasensor.

In this work, we report a novel method for the label-free detection of cyanotoxin molecules based on a direct assay utilizing a graphene-modified surface plasmon resonance (SPR) aptasensor. Molecular dynamic simulation of the aptamer's interaction with cylindrospermopsin (CYN) reveals the strongest binding sites between C18-C26 pairs. To modify the SPR sensor, the wet transfer method of CVD monolayer graphene was used. For the first time, we report the use of graphene functionalized by an aptamer as a bioreceptor in conjunction with SPR for the detection of CYN. In a direct assay with an anti-CYN aptamer, we demonstrated a noticeable change in the optical signal in response to the concentrations far below the maximum tolerable level of 1 µg/L and high specificity.

Nanopores/Nanochannels Based on Electrical and Optical Dual Signal Response for Application in Biological Detection†

Comprehensive SummaryCancers and chronic diseases have always been global health problems. The occurrence and development of such diseases are closely related to the abnormalities of proteins, nucleic acids, ions or small molecules in the body. Nowadays, nanopores/nanochannels have emerged as a powerful platform for detecting these biomolecules based on the electrical signal variation caused by biomolecules passing. However, detection relied on the electrical signal easily suffered from the clogging defects, low throughput, and strong background signals. Fortunately, the emergence of designing nanopores/nanochannels based on electrical and optical dual signal response has brought innovative impetus to biological detection, which can also identify the chemical compositions and conformations of the biomolecules. In this review, we summarize the reasonable preparation of nanopores/nanochannels with electrical and optical dual signal response and their application in biological detection. According to different biomolecules, we divide the targets into four types, including nucleic acids, small molecules, ions and proteins. In each section, the design of representative examples and the principle of dual signal generation are introduced and discussed. Finally, the prospects and challenges of nanopores/nanochannels based on electrical and optical dual signal response are also discussed.

Enantiomorphic Single Crystals of Linear Lead(II) Bromide Perovskitoids with White Circularly Polarized Emission

AbstractChiroptical hybrid organic–inorganic perovskites are emerging as a new class of promising materials with mirror optical signal responses for optoelectronic applications. However, chiroptical white‐emission materials have been scarcely unearthed. Herein, four pairs of hybrid lead(II) bromide perovskitoids were obtained, namely, (R)‐ and (S)‐(H2MPz)PbBr4 (R/S‐MPz=(R)‐(−)/(S)‐(+)‐2‐methylpiperazine) (1 and 2), (R)‐ and (S)‐(H2MPz)3Pb2Br10⋅2 DMAc (3 and 4), (R)‐ and (S)‐(H2MPz)PbBr4⋅0.5 MeCN (5 and 6) and (R)‐ and (S)‐(H2MPz)2Pb2Br8⋅DCM (7 and 8). Notably, they all exhibit ultrabroadband emission and chiroptical signals. Perovskitoids 3–6 even achieve white circularly polarized emission with a high dissymmetric factor (glum) (±3×10−3 for 3 and 4; ±8×10−3 for 5 and 6). This new type of hybrid perovskitoids will attract attention and find applications in chiroptical fields because of the extensively and easily tunable photophysical properties.

Enantiomorphic Single Crystals of Linear Lead(II) Bromide Perovskitoids with White Circularly Polarized Emission.

Chiroptical hybrid organic-inorganic perovskites are emerging as a new class of promising materials with mirror optical signal responses for optoelectronic applications. However, chiroptical white-emission materials have been scarcely unearthed. Herein, four pairs of hybrid lead(II) bromide perovskitoids were obtained, namely, (R)- and (S)-(H2 MPz)PbBr4 (R/S-MPz=(R)-(-)/(S)-(+)-2-methylpiperazine) (1 and 2), (R)- and (S)-(H2 MPz)3 Pb2 Br10 ⋅2 DMAc (3 and 4), (R)- and (S)-(H2 MPz)PbBr4 ⋅0.5 MeCN (5 and 6) and (R)- and (S)-(H2 MPz)2 Pb2 Br8 ⋅DCM (7 and 8). Notably, they all exhibit ultrabroadband emission and chiroptical signals. Perovskitoids 3-6 even achieve white circularly polarized emission with a high dissymmetric factor (glum ) (±3×10-3 for 3 and 4; ±8×10-3 for 5 and 6). This new type of hybrid perovskitoids will attract attention and find applications in chiroptical fields because of the extensively and easily tunable photophysical properties.

Introduction of quorum sensing elements into bacterial bioreporter circuits enhances explosives' detection capabilities.

A possible solution for the standoff detection of buried landmines is based on the use of microbial bioreporters, genetically engineered to emit a remotely detectable optical signal in response to trace amounts of explosives’ signature chemicals, mostly 2,4‐dinitrotoluene (DNT). Previously developed DNT sensor strains were based on the fusion of a DNT‐inducible gene promoter to a reporting element, either a fluorescent protein gene or a bacterial bioluminescence gene cassette. In the present study, a different approach was used: the DNT‐inducible promoter activates, in Escherichia coli, the quorum‐sensing luxI and luxR genes of Aliivibrio fischeri. N‐Acyl homoserine lactone (AHL), synthesized by LuxI, combines with LuxR and activates the bioluminescence reporter genes. The resulting bioreporter displayed a dose‐dependent luminescent signal in the presence of DNT. Performance of the sensor strain was further enhanced by manipulation of the sensing element (combining the E. coli DNT‐inducible azoR and yqjF gene promoters), by replacing the luminescence gene cassette of Photorhabdus luminescens luxCDABE with A. fischeri luxCDABEG, and by introducing two mutations, eutE and ygdD, into the host strain. DNT detection sensitivity of the final bioreporter was over 340‐fold higher than the original construct.

Dual‐Channel Flexible Strain Sensors Based on Mechanofluorescent and Conductive Hydrogel Laminates

AbstractFlexible strain sensors are of great importance in many emerging applications for human motion monitoring, implanted devices, and human–machine interactive systems. However, the dual‐channel sensing systems that enable both strain‐dependent electronic and visually optical signal responses still remain underdeveloped, but such systems are of great interest for human–machine interactive uses. Here, inspired by the mechanically modulated skin color changes of squids via muscle contracting/releasing movements, a class of mechanofluorescent and conductive hydrogel laminates for visually flexible electronics is presented. The sensing laminates consist of interfacially bonded red fluorescent hydrogel, polydimethylsiloxane and carbon nanotubes (CNTs) film. Since the densely stacked microscopic CNTs film can be precisely stretched to induce the formation of network microcracks, the developed hydrogel laminates are endowed with simultaneous fluorescence‐color and resistance changes, which can function as dual‐channel flexible sensors for real‐time human motion monitoring. These properties make the bioinspired soft hydrogel laminate electronics quite promising in the flexible electronics field.

Nanostructured Shell-Layer Artificial Antibody with Fluorescence-Tagged Recognition Sites for the Trace Detection of Heavy Metal Ions by Self-Reporting Microsensor Arrays.

Herein, a strategy for a metal ion-imprinted artificial antibody with recognition sites tagged by fluorescein was carried out to construct the selective sites with a sensitive optical response signal to the specific metal ion. The synthesized silica nanoparticles were modified by the derivative residue group of 3-aminopropyltriethoxysilane conjugated with a 4-chloro-7-nitro-1,2,3-benzoxadiazole (NBD-Cl) molecule through the hydrolysis and condensation reactions. The as-prepared silica nanoparticles were encapsulated by metal ion (Cu2+, Cd2+, Hg2+, and Pb2+)-imprinted polymers with nanostructured layers through the copolymerization of ethyl glycol dimethyl methacrylate (EGDMA) as a cross-linker, AIBN as an initiator, metal ions as template molecules, AA as a functional monomer, and acetonitrile as a solvent. The layers of molecular imprinted polymers (MIPs) with a core-shell structure removed template molecules by EDTA-2Na to retain the cavities and spatial sizes to match the imprinted metal ions. The microsensor arrays were achieved by the self-assembly technique of SiO2@MIP nanoparticles on the etched silicon wafer with regular dot arrays. The nanostructured-shell layers with fluorescence-tagged recognition sites rebound metal ions by the driving force of concentration difference demonstrates the high selective recognition and sensitive detection to heavy metal ions through the decline of fluorescence intensity. The LOD concentration for four metal ions is down to 10-9 mol·L-1. The method will provide biomimetic synthesis, analyte screen, and detection of highly dangerous materials in the environment for theoretical foundation and technological support.

Sensorless LED display screen interaction and object recognition

AbstractTaking advantage of the photoelectric characteristics of LED other than the light‐emitting function, this paper proposes a light sensing detection method and system without adding additional sensors to the LED screen. A two‐pole detection structure with a function of detecting positive and negative voltage is introduced to the LED drive circuit, which ensures the high‐speed characteristics during detection. What's more, the LED is controlled to work in photoconductive mode to obtain high voltage sensitivity when the intensity of incident light changes. The proposed module can reach an optical signal response rate of 19.1 μs with a detection rate of 23.5 Hz without affecting the original display function. The optical signal detection can reach a voltage sensitivity of 3.02 mV per lx. To verify the photoelectric detection capability of the method presented in this paper, a brand‐new screen object recognition system is built and tested. An 8 × 8 LED display module is used in experiment, and the scale of LED screen can be expanded easily and flexibly. In an ideal environment, a recognition accuracy of 99.25% can be achieved, while the recognition accuracy can still reach over 96.5% in a complex light environment. Therefore, this work has further application possibilities for light interaction and fast object recognition in large screens.

Spectral-Phase Interferometry Detection of Ochratoxin A via Aptamer-Functionalized Graphene Coated Glass.

In this work, we report a novel method of label-free detection of small molecules based on direct observation of interferometric signal change in graphene-modified glasses. The interferometric sensor chips are fabricated via a conventional wet transfer method of CVD-grown graphene onto the glass coverslips, lowering the device cost and allowing for upscaling the sensor fabrication. For the first time, we report the use of graphene functionalized by the aptamer as the bioreceptor, in conjunction with Spectral-Phase Interferometry (SPI) for detection of ochratoxin A (OTA). In a direct assay with an OTA-specific aptamer, we demonstrated a quick and significant change of the optical signal in response to the maximum tolerable level of OTA concentration. The sensor regeneration is possible in urea solution. The developed platform enables a direct method of kinetic analysis of small molecules using a low-cost optical chip with a graphene-aptamer sensing layer.

Optical recording of brain functions based on voltage-sensitive dyes

To better understand the spatial distribution of brain functions, we need to monitor and analyze neuronal activities. Electrophysiological technique has provided an important method for the exploration of some neural circuits. However, this method cannot simultaneously detect the activities of nerve cell groups. Therefore, methods that can monitor the spatial distribution of neuronal population activity are demanded to explore brain functions. Voltage-sensitive dyes (VSDs) shift their absorption or emission optical signals in response to different membrane potentials, allowing assessing the global electrical state of neurons. Optical recording technique coupled with VSDs is a promising method to monitor the brain functions by detecting optical signal changes. This review focuses on the fast and slow responses of VSDs to membrane potential changes and optical recordings utilized in the central nervous system. In this review, we attempt to show how VSDs and optical recordings can be used to obtain brain functional monitoring at high spatial and temporal resolution. Understanding of brain functions will not only greatly improve the cognition of information transmission of complex neural network, but also provide new methods of treating brain diseases such as Parkinson’s and Alzheimer’s diseases.

Compact Laser Driver for Ultrasonic Arbitrary Position and Width Pulse Sequences Generation

Laser ultrasound offers several benefits in comparison to immersion or air-coupled ultrasound: it directly generates stress on the sample surface; it has a wide bandwidth and a small acoustic source can be produced. Conventionally, high-power pulsed lasers are required therefore equipment is bulky and expensive. Here we propose to use mid-power laser diodes, which are small and low cost. To solve the low signal amplitude problem with lower power lasers, the use of spread spectrum signal, arbitrary position, and width binary pulse sets is proposed. To date, a laser driver for this task has not been available. This article describes the development of such a compact driver, where the essential electronics occupy an area of $10\,\,\times20$ mm. The whole system with a fixture for kinematic mount is comparable in size to a conventional piezoelectric ultrasonic transducer. The driver can supply pulse sets of up to 40 A. Individual pulse duration can vary between 20 and 1000 ns (0.5–25-MHz ultrasound range) and the total pulse train duration is limited by the laser type used. Experiments show that up to 10- $\mu \text{s}$ long pulse sets can be used at 10-A current, without laser degradation. Current waveforms, beam profile, and optical response signals were measured for three rectified topologies. It was concluded that the GaN-based constant current switch topology has the best performance, but a power MOSFET in a source current feedback topology can also be used to generate pulses down to 20 ns. Photoacoustic response signals from chirp and phase shift keying modulation have been demonstrated.

Triple-dimensional spectroscopy combined with chemometrics for the discrimination of pesticide residues based on ionic liquid-stabilized Mn-ZnS quantum dots and covalent organic frameworks

Manganese-doped zinc sulfide quantum dots (Mn-ZnS QDs) are promising candidates for multi-channel sensing analysis due to their multi-dimensional optical properties. In this study, we integrated amino-silane and ionic liquid co-modified Mn-ZnS QDs and covalent organic frameworks (COFs) into optosensing nanoparticles to provide triple-dimensional optical response signals and combined them with chemometrics for the analysis of multiple pesticide residues. Through the exploration and optimization of a series of conditions, fluorescence, room temperature phosphorescence, and ultraviolet−visible combined with chemometrics were used for the discrimination and recognition of multiple pesticide residues in fruits and vegetables. The ionic liquid of 1-vinyl-3-ethylimidazolium tetrafluoroborate was used to modify Mn-ZnS QDs to improve the optical response and enrichment of pesticide adsorption sites, which were also synergistically enhanced by the COF support. This is a potential method to discriminate pesticides efficiently and enables fast and reliable analysis of pesticides in the agricultural and food industries.

Genome-wide gene-deletion screening identifies mutations that significantly enhance explosives vapor detection by a microbial sensor

Genetically engineered microbial biosensors, capable of detecting traces of explosives residues above buried military ordnance and emitting an optical signal in response, may potentially serve for the standoff detection of buried landmines. A promising candidate for such an application is a previously reported Escherichia coli-based reporter strain that employs the yqjF gene promoter as its sensing element; however, for this sensor to be able to detect actual landmines reliably, it was necessary for its detection sensitivity and signal intensity to be enhanced. In this study, a high-throughput approach was employed to screen the effects of individual gene deletions on yqjF activation by 2,4-dinitrotoluene (DNT). Several genes were identified, the deletion of which elicited a significant enhancement of yqjF induction by DNT. The most promising of these mutations were introduced into the sensor strain, individually or in pairs, yielding a considerable increase in signal intensity and a lowering of the detection threshold. A strain harboring two of the identified mutations, ygdD and eutE, appears to be the most sensitive microbial biosensor currently described for the detection of traces of landmine explosives.

Shielded Silver Nanorods for Bioapplications.

Silver is arguably the best plasmonic material in terms of optical performance. However, wide application of Ag and Ag-containing nanoparticles is usually hindered by two major drawbacks, namely, chemical degradation and cytotoxicity. We report herein a synthetic method for highly monodisperse polymer-coated Ag nanorods, which are thereby protected against external stimuli (oxidation, light, heat) and are noncytotoxic to various cell lines. The monodispersity of Ag nanorods endows them with narrow plasmon bands, which are tunable into the near-infrared biological transparency window, thus facilitating application in bioanalytical and therapeutic techniques. We demonstrate intracellular surface-enhanced Raman scattering (SERS) imaging using Ag nanorods encoded with five different Raman reporter molecules. Encoded Ag nanorods display long-term stability in terms of size, shape, optical response, and SERS signal. Our results help eliminate concerns of instability and cytotoxicity in the application of Ag-containing nanoparticles with enhanced optical response, toward the development of bioapplications.