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Abstract Excessively tilted fiber gratings (ExTFGs) are a type of special optical fiber grating device different from traditional fiber Bragg gratings, long period fiber gratings, and tilted fiber Bragg gratings. Due to the excessively tilted fiber fringe structure in the fiber core, ExTFGs could couple the light of the core mode into the high-order forward-propagating cladding modes, which would split into two sets of polarization dependent modes resulting in dual-peak resonances in the transmission spectrum. ExTFGs have the properties of the high refractive index sensitivity and low thermal crosstalk, which makes them very suitable for biochemical sensing applications. This paper will review the development of ExTFGs in terms of the mode coupling behavior, spectra characteristic, especially the refractive index sensitivity enhancement, biochemical modification methods of the sensor, and their applications in the bio-chemical sensing area, including pondus hydrogenii (pH) heavy metal ions, humidity, glucose, and immune sensing for various animal virus and biomarkers. Moreover, several composite sensing structures based on ExTFGs will be summarized.

Multi-band circular dichroism (CD) response and tunability on the chiral metasurface are crucial for this device's applications in sensing and detection. This work proposes a dual-band CD Au-CaF2-Au dimer elliptical metasurface absorber, where chiroptical sensing is realized by breaking the geometric symmetry between two ellipses. The proposed metasurface can achieve high CD values of 0.8 and −0.74 for the dual-band within the 3–5 μm region, and the CD values can be manipulated by independently adjusting the geometric parameters of the metasurface. Furthermore, a slotted nanocircuit is introduced onto the metasurface to enhance its tunability by manipulating the geometry parameter in the design process, and the related mechanism is explained using an equivalent circuit model. The simulation of the sensing model revealed that the slotted nanocircuit enhances the sensor's tunability and significantly improves its bandwidth and sensitivity, achieving peak enhancements at approximately 753 nm and 1311 nm/RIU, respectively. Due to the strong dual-band positive (and negative) responses of the CD values, flexible wavelength tunability, and nonlinear sensitivity enhancement, this design provides a new approach for the development and application of mid-infrared chiroptical devices. [ABSTRACT FROM AUTHOR]

Laser-scribed graphene (LSG), a classic three-dimensional porous carbon nanomaterial, is directly fabricated by laser irradiation of substrate materials. Benefiting from its excellent electrical and mechanical properties, along with flexible and simple preparation process, LSG has played a significant role in the field of flexible sensors. This review provides an overview of the critical factors in fabrication, and methods for enhancing the functionality of LSG. It also highlights progress and trends in LSG-based sensors for monitoring physiological indicators, with an emphasis on device fabrication, signal transduction, and sensing characteristics. Finally, we offer insights into the current challenges and future prospects of LSG-based sensors for health monitoring and disease diagnosis. [ABSTRACT FROM AUTHOR]

[Display omitted] • Enabling fabrication and exposure of merely graphene edges. • Utilizing quantum capacitance proportional to the density of states at edges. • Singular electrical field gradients at edges for trapping biomolecules. • Detecting biomolecules at 10 ag/mL concentrations within several minutes. Graphene, with its outstanding electrical properties, has appealed to the attention of researchers all over the world for biosensing applications. So far, much of the research has been conducted on the field-effect modulations of carriers in the basal plane of graphene after adsorbing charged biomolecules. However, another essential aspect--the graphene edge--has been largely ignored due to the difficulties in both manufacture and characterization. Here, we propose a facile intercalation and pressure sintering approach that enables the fabrication and exposure of only graphene edges. The quantum capacitance of the exposed edges is proportional to the local density of state (DOS) and can be harvested for biochemical sensing. Notably, due to fringe electric field enhancement and biomolecular convergence at the one-dimensional graphene edges, we are able to detect four representative amino acids at 0.01 fg/mL concentrations within several minutes. These achievements in innovative quantum capacitance measurements of graphene edges, combined with simple and robust device fabrication by eliminating complex micro-nano processing, offer a new avenue for the next generation of biochemical sensors with ever-demanding sensitivities. [ABSTRACT FROM AUTHOR]

Excessively tilted fiber gratings (ExTFGs) are a type of special optical fiber grating device different from traditional fiber Bragg gratings, long period fiber gratings, and tilted fiber Bragg gratings. Due to the excessively tilted fiber fringe structure in the fiber core, ExTFGs could couple the light of the core mode into the high-order forward-propagating cladding modes, which would split into two sets of polarization dependent modes resulting in dual-peak resonances in the transmission spectrum. ExTFGs have the properties of the high refractive index sensitivity and low thermal crosstalk, which makes them very suitable for biochemical sensing applications. This paper will review the development of ExTFGs in terms of the mode coupling behavior, spectra characteristic, especially the refractive index sensitivity enhancement, biochemical modification methods of the sensor, and their applications in the bio-chemical sensing area, including pondus hydrogenii (pH) heavy metal ions, humidity, glucose, and immune sensing for various animal virus and biomarkers. Moreover, several composite sensing structures based on ExTFGs will be summarized. [ABSTRACT FROM AUTHOR]

Multi-band circular dichroism (CD) response and tunability on the chiral metasurface are crucial for this device’s applications in sensing and detection. This work proposes a dual-band CD Au-CaF2-Au dimer elliptical metasurface absorber, where chiroptical sensing is realized by breaking the geometric symmetry between two ellipses. The proposed metasurface can achieve high CD values of 0.8 and −0.74 for the dual-band within the 3–5 μm region, and the CD values can be manipulated by independently adjusting the geometric parameters of the metasurface. Furthermore, a slotted nanocircuit is introduced onto the metasurface to enhance its tunability by manipulating the geometry parameter in the design process, and the related mechanism is explained using an equivalent circuit model. The simulation of the sensing model revealed that the slotted nanocircuit enhances the sensor’s tunability and significantly improves its bandwidth and sensitivity, achieving peak enhancements at approximately 753 nm and 1311 nm/RIU, respectively. Due to the strong dual-band positive (and negative) responses of the CD values, flexible wavelength tunability, and nonlinear sensitivity enhancement, this design provides a new approach for the development and application of mid-infrared chiroptical devices.

Laser-scribed graphene (LSG), a classic three-dimensional porous carbon nanomaterial, is directly fabricated by laser irradiation of substrate materials. Benefiting from its excellent electrical and mechanical properties, along with flexible and simple preparation process, LSG has played a significant role in the field of flexible sensors. This review provides an overview of the critical factors in fabrication, and methods for enhancing the functionality of LSG. It also highlights progress and trends in LSG-based sensors for monitoring physiological indicators, with an emphasis on device fabrication, signal transduction, and sensing characteristics. Finally, we offer insights into the current challenges and future prospects of LSG-based sensors for health monitoring and disease diagnosis.

Soft (flexible and stretchable) biosensors have great potential in real-time and continuous health monitoring of various physiological factors, mainly due to their better conformability to soft human tissues and organs, which maximizes data fidelity and minimizes biological interference. Most of the early soft sensors focused on sensing physical signals. Recently, it is becoming a trend that novel soft sensors are developed to sense and monitor biochemical signals in situ in real biological environments, thus providing much more meaningful data for studying fundamental biology and diagnosing diverse health conditions. This is essential to decentralize the healthcare resources towards predictive medicine and better disease management. To meet the requirements of mechanical softness and complex biosensing, unconventional materials, and manufacturing process are demanded in developing biosensors. In this review, we summarize the fundamental approaches and the latest and representative design and fabrication to engineer soft electronics (flexible and stretchable) for wearable and implantable biochemical sensing. We will review the rational design and ingenious integration of stretchable materials, structures, and signal transducers in different application scenarios to fabricate high-performance soft biosensors. Focus is also given to how these novel biosensors can be integrated into diverse important physiological environments and scenarios in situ , such as sweat analysis, wound monitoring, and neurochemical sensing. We also rethink and discuss the current limitations, challenges, and prospects of soft biosensors. This review holds significant importance for researchers and engineers, as it assists in comprehending the overarching trends and pivotal issues within the realm of designing and manufacturing soft electronics for biochemical sensing.

A specific structural multiband terahertz (THz) metamaterial sensor (TMS) was designed herein to improve the sensitivity of detecting multiple trace fluoroquinolone (FQ) antibiotics in water, and a multiple resonance response competition and selection fusion (MRR-CSF) framework was proposed for accurate FQ analysis. The TMS based on three-concentric C4-symmetrical split-ring (TC4) structures generated five bands at 0.797, 0.900, 1.097, 1.198, and 1.777 THz. The multiband resonance signals for three types of FQs, including enrofloxacin (ENR), pefloxacin (PEF), and nadifloxacin (NAD), were detected by the TMS, which increased as the antibiotic concentrations increased (5–140 ng/L). The proposed method can solve the problems of low accuracy and poor robustness of conventional single-response regression by combining selected and fused TMS-effective resonance response variables with three multivariate regression strategies. The calculated comprehensive metrics also provide an objective evaluation of multiband TMS performance. The designed TMS combined with the proposed MRR-CSF framework showed 21 %–27 %, 13 %–17 %, and 12 %–13 % improvements in the detection accuracy for ENR, PEF, and NAD, respectively, according to the univariate regression results. The limit of detection for the ENR, PEF, and NAD antibiotic solutions was achieved at 5 ng/L, and the reliable range of recoveries (100 % ± 25 %), average recoveries (>90 %), and relative standard deviation values (<5 %) were obtained for the concentration prediction of newly prepared FQs. This study demonstrates the promising prospect of applying the multiband TMS combined with the MRR-CSF framework for accurate biochemical sensing and detection. • A multi-band THz metamaterial sensor was prepared for trace FQs detection. • A multivariate fusion framework was proposed to enhance detection accuracy. • The proposed method outperformed all univariate regressions in improving accuracy. • The detection limit of antibiotic reached 5 ng/L by proposed method. [ABSTRACT FROM AUTHOR]

Laser scribing is a technique that converts carbon-rich precursors into 3D-graphene nanomaterial via direct, single-step, and maskless laser writing in environmental conditions and using a scalable approach. It allows simple, fast, and reagentless production of a promising material with outstanding physicochemical features to create novel electrochemical sensors and biosensors. This review addresses different strategies for fabricating laser-scribed graphene (LSG) devices and their association with nanomaterials, polymers, and biological molecules. We provide an overview of their applications in environmental and health monitoring, food safety, and clinical diagnosis. The advantages of their integration with machine learning models to achieve low bias and enhance accuracy for data analysis is also addressed. Finally, in this review our insights into current challenges and perspectives for LSG electrochemical sensors are presented. [ABSTRACT FROM AUTHOR]

Optical spectroscopy supporting studies of the absorption and emission of light by matter is a widely used tool in analytical science. Recently, optical spectrometers have shown tremendous improvement on spectral resolution, accuracy, sensitivity, as well as miniaturization. However, most of them still only focus on single or few sensing modes, thus limiting their practical applications especially in complex sensing conditions. To extend applications, integrating with absorption, emission, and surface plasmon resonance (SPR) spectroscopy detecting systems, a multipurpose optical fiber smartphone spectrometer (MOSS) is designed to provide a point-of-care testing platform for on-site biochemical sensing. The MOSS is compact only with the size of $167\times 75\times85$ mm3 but has excellent sensing performance. It reaches extremely high spectral resolution as $\approx 10$ nm and has been successfully applied in nitrite, mercury ion, and sucrose sensing. In addition, the MOSS is equipped with inner power supply and user-friendly smartphone application, especially suiting for on-site applications. Since the MOSS can support high-quality multipurpose spectral detection but only using compact and cost-effective devices, it can be a potential point-of-care testing platform especially for biochemical sensing applications. [ABSTRACT FROM AUTHOR]

A silicon grating based highly sensitive nanophotonic device is proposed for biochemical sensing. Gratings are etched on the SOI rib waveguide and the dimensions of the device are optimized to enhance the sensitivity. The proposed device is a narrowband photonic filter with evanescent based Bragg gratings. The rigorous numerical analysis has been performed to evaluate the sensing capabilities of the proposed photonic biochemical sensing device. The device has been designed to operate at a wavelength of 1550 nm. The results show a high sensitivity of 770 nm/RIU with a Full Width Half Maxima (FWHM) of 7.5 nm and a figure of merit (FOM) of 103/RIU. The device is ultra-compact with a footprint area of 12.5 μm2. Further, the sensing ability for various bio-analytes has been analyzed which shows optimum performance of the proposed biochemical sensing device. [ABSTRACT FROM AUTHOR]

Advancements in robotic surgery help to improve the endoluminal diagnosis and treatment with minimally invasive or non-invasive intervention in a precise and safe manner. Miniaturized probe-based sensors can be used to obtain information about endoluminal anatomy, and they can be integrated with medical robots to augment the convenience of robotic operations. The tremendous benefit of having this physiological information during the intervention has led to the development of a variety of in vivo sensing technologies over the past decades. In this paper, we review the probe-based sensing techniques for the in vivo physical and biochemical sensing in China in recent years, especially on in vivo force sensing, temperature sensing, optical coherence tomography/photoacoustic/ultrasound imaging, chemical sensing, and biomarker sensing. [ABSTRACT FROM AUTHOR]

This overview concerns recent patents and patented technologies in relation to the development of hydrogel-based biosensors, published until 2022. As a result, 257 patent documents and 145 simple patent families have been searched through different specialized patent databases. Furthermore, the patent classification confirmed that the most claimed inventions concern chemical analysis of biological material and biospecific binding assay materials with an insoluble carrier for immobilizing immunochemicals. Overall, the research, development, and innovation concerning hydrogel-based biosensors are based on improvements in the synthesis of hydrogels, biomolecule immobilization and detection, as well as microelectronic device integration and microfabrication techniques. A collection of recent patented technologies is proposed at the end. In this respect, it aimed to demonstrate the potential trends and challenges in relation to the development of hydrogel-based biosensors.

A hybrid plasmonic transducer made of a Poly‐(ethylene glycol) diacrylate (PEGDA) hydrogel and citrate gold nanoparticles detects the biotin‐streptavidin interaction at picomolar (× 10−12m) concentrations. The all‐solution fabrication strategy, herein proposed, is large‐scale, easily tunable, and low‐cost; nevertheless, this innovative device is highly reproducible and optically stable, and it can be used in dual‐optical mode. Indeed, both metal‐enhanced fluorescence and localized surface plasmon resonance signals can be exploited to quantify the biorecognition process in a 3D architecture. The large swelling capability of high molecular weight PEGDA is used to investigate the plasmon absorption variations resulting from the exposure to biological solutions containing high molecular weight molecules within the 3D network. The proposed transducer represents a low‐cost, flexible, and easy‐to‐use platform for sensing applications in biomedical or environmental diagnostics. [ABSTRACT FROM AUTHOR]

The effect of pH on the performance of undoped silicon carbide nanowire field-effect transistors (SiCNW-FETs) was systematically studied using various solutions with pH ranging from pH 2 to pH 13 and important transport parameters such as transconductance, mobility, and resistivity were reported. Interestingly, at 2 V, alkaline solutions with high pH value (pH 13) revealed a higher transconductance of 7.13 nS and lower resistivity of 40 Ω cm as compared to acidic solutions with 0.01 nS and 2.1x104 Ω cm at pH 2, respectively. A model describing the pH-dependent conductance of the SiCNW-FETs was proposed. Moreover, a comprehensive comparison of the pH effects on the transport properties of the undoped SiCNW-FETs and nitrogen-doped SiCNW-FET was presented and the measurements clearly revealed opposite trends for a wide range of pH solutions. In short, our SiCNW-FETs with high sensitivity, high stability, and minuscule sample volume can provide solutions for the development of harsh environment compatible nanosensors for chemical, biochemical, and environmental sensing applications. [ABSTRACT FROM AUTHOR]

Abstract Single atomically thick graphene, with unique structural flexibility, surface sensitivity, and effective light-mater interaction, has shown exceptional advances in optoelectronics. It opens a door for diverse functionalized photonic devices, ranging from passive polarizers to active lasers and parametric oscillators. Among them, graphene-fiber biochemical sensors combine the merits of both graphene and fiber structures, demonstrating impressively high performances, such as single-molecule detectability and fast responsibility. These graphene-fiber biochemical sensors can offer tools in various applications, such as gas tracing, chemical analysis, and medical testing. In this paper, we review the emerging graphene-fiber biochemical sensors comprehensively, including the sensing principles, device fabrications, systematic implementations, and advanced applications. Finally, we summarize the state-of-the-art graphene-fiber biochemical sensors and put forward our outlooks on the development in the future.

3D-printed portable devices have immense and proven potential to transform the field of electrochemiluminescence (ECL) for diverse biochemical applications. 3D printing (3DP) offers unparalleled ability to build tiny devices in a single step with high accuracy and compatibility, and integrability as per the requirement. In this study, for the first time, a six-well 3D-printed closed bipolar electrochemiluminescence (3DP-CBPE-ECL) device has been successfully fabricated and validated by performing single-step detection of various biochemicals such as glucose and choline. Luminol/H2O2-based enzymatic reactions were performed with optimized parameters for selective sensing of glucose and choline. The single-step detection of glucose and choline was accomplished for the linear ranges of 0.1 to 10 mM and 0.1 to 5 mM, with a limit of detections (LODs) of 24 µM and 10 µM, respectively. A smartphone was leveraged to execute multiple activities such as powering the ECL device, capturing ECL images, and calculating the ECL intensity of the obtained ECL signal. The feasibility of a six-well 3DP-CBPE-ECL device was tested by sensing glucose and choline simultaneously in a single device at three different concentrations. Furthermore, the concentration of glucose and choline was calculated in real blood serum using the conventional additive (spiking) method, demonstrating the high practicability of the fabricated ECL device and yielding promising findings. Finally, based on the obtained results and other advantages such as low-cost, fast prototyping and requirement of a minimum sample volume, the fabricated six-well 3DP-CBPE-ECL device has shown potential to be used in the field of biochemical applications. [ABSTRACT FROM AUTHOR]

The steadily increasing demand for accurate analysis of vitamin D level, via measurement of its best general marker, 25-hydroxyvitamin D (25(OH)D), pushes for the development of novel automated assays capable of working at very low concentrations. Here, we propose a plasmonic biosensor of 25(OH)D3 (calcifediol) based on surface-enhanced infrared absorption spectroscopy, which exploits the resonant coupling between plasmonic nanoantennas and vibrational excitation of small molecules. Specifically, our proposed platform features a large-area (several mm2) metasurface made of gold nanoantennas fabricated on a silicon substrate, comprising different macroregions (“pixels”) of area 500 × 500 µm2. In each pixel, the nanoantenna geometrical parameters are tuned so as to support localized surface plasmon resonances (and hence large field enhancements at the nanoscale) within different regions of the infrared spectrum. As a result, a single chip is capable of performing analysis from the region of functional groups to that of fingerprint. Two different designs are fabricated via electron beam lithography, functionalized with a correlated antibody for the detection of 25(OH)D3, and characterized via Fourier-transform infrared spectroscopy. Our experiments demonstrate the capability to detect a concentration as low as 86 pmol/L, and an amount of immobilized small molecules of 25(OH)D3 monohydrate (molecular weight: 418.65 g/mol) as low as 4.31 amol over an area of 100 × 100 µm2.

Motor complication management is one of the main unmet needs in Parkinson's disease patients. Among the most promising emerging approaches for handling motor complications in Parkinson's disease, adaptive deep brain stimulation strategies operating in closed-loop have emerged as pivotal to deliver sustained, near-to-physiological inputs to dysfunctional basal ganglia-cortical circuits over time. Existing sensing systems that can provide feedback signals to close the loop include biochemical-, neurophysiological- or wearable-sensors. Biochemical sensing allows to directly monitor the pharmacokinetic and pharmacodynamic of antiparkinsonian drugs and metabolites. Neurophysiological sensing relies on neurotechnologies to sense cortical or subcortical brain activity and extract real-time correlates of symptom intensity or symptom control during DBS. A more direct representation of the symptom state, particularly the phenomenological differentiation and quantification of motor symptoms, can be realized via wearable sensor technology. Biochemical, neurophysiologic, and wearable-based biomarkers are promising technological tools that either individually or in combination could guide adaptive therapy for Parkinson's disease motor symptoms in the future. [ABSTRACT FROM AUTHOR]

Laser scribing is a technique that converts carbon-rich precursors into 3D-graphene nanomaterial via direct, single-step, and maskless laser writing in environmental conditions and using a scalable approach. It allows simple, fast, and reagentless production of a promising material with outstanding physicochemical features to create novel electrochemical sensors and biosensors. This review addresses different strategies for fabricating laser-scribed graphene (LSG) devices and their association with nanomaterials, polymers, and biological molecules. We provide an overview of their applications in environmental and health monitoring, food safety, and clinical diagnosis. The advantages of their integration with machine learning models to achieve low bias and enhance accuracy for data analysis is also addressed. Finally, in this review our insights into current challenges and perspectives for LSG electrochemical sensors are presented.

Advancements in robotic surgery help to improve the endoluminal diagnosis and treatment with minimally invasive or non-invasive intervention in a precise and safe manner. Miniaturized probe-based sensors can be used to obtain information about endoluminal anatomy, and they can be integrated with medical robots to augment the convenience of robotic operations. The tremendous benefit of having this physiological information during the intervention has led to the development of a variety of in vivo sensing technologies over the past decades. In this paper, we review the probe-based sensing techniques for the in vivo physical and biochemical sensing in China in recent years, especially on in vivo force sensing, temperature sensing, optical coherence tomography/photoacoustic/ultrasound imaging, chemical sensing, and biomarker sensing.

Biochemical sensing plays a vital role in the research of life and natural science. However, with the increase of environmental complexity and amount of sample, traditional sensors cannot meet the needs of accurate and efficient analysis of numerous data. The emergence of AI provides a new strategy for overcoming the challenges in biochemical sensing, especially in the field of molecular diagnosis and imaging analysis. In this review, we focus on how AI reinforce biochemical sensing in accuracy, sensitivity, specificity, and efficiency. The applications of AI in material synthesis, molecular diagnosis and imaging analysis in the past three years are reviewed, and the characteristics and performance evaluation methods of the algorithms are emphatically discussed. Finally, we proposed the challenges of AI biochemical sensing in application, including database construction, reasonable selection of algorithms, and data reliability verification, and clarified the advancements needed and future development prospects. • How AI can benefit biochemical sensors. • Overview of characteristics and evaluation methods of AI algorithms. • The challenges of AI in the application of biochemical sensors. [ABSTRACT FROM AUTHOR]

We present a new quasi D-shaped plasmonic photonic crystal fiber (PCF) microsensor with dual polarization for back-to-back measurement of refractive index (RI) and temperature. The PCF structure of the microsensor is form birefringent and supports two orthogonal polarizations for independent probing of both RI and temperature variations. Thin layers of tantalum pentoxide (Ta2O5) and gold (Au) are applied to the side-polished plane to form the RI sensing section. Furthermore, four micro air holes in the lower part of its outer cladding ring are gold-coated and selectively infiltrated with a temperature-sensitive liquid. A detailed investigation and numerical analyses of the coupling characteristics and sensing responses are presented using the finite element method (FEM) with a circular perfectly matched layer (PML). The RI metrics show a maximum wavelength sensitivity of 5000 nm/RIU and a maximum amplitude sensitivity of 266.54 RIU−1 from 1.35 to 1.46 RI range in the specified operating wavelength range of 1.25- $1.65~\mu \text{m}$. The corresponding RI resolution is $2.0\times 10^{-5}$ RIU. For the temperature sensing metrics, a maximum amplitude sensitivity of $4.8\times 10^{-2}\,\,^\circ \text{C}^{-1}$ , a maximum wavelength sensitivity of 3.0 nm/°C, and a maximum resolution of $3.33\times 10^{-2}\,\,^{\circ }\text{C}$ from −50°C to 50°C is achieved. With appropriate instrumentation incorporating a polarization selector, the microsensor can double as a real-time simultaneous multiparameter sensor. Applications for the proposed microsensor can be found in molecular science, medical measurement and analysis, terrestrial environmental engineering and data assessment, aquatic ecosystem investigations, pharmaceutical and alimentary process control and validation, cryogenic studies, and several others. [ABSTRACT FROM AUTHOR]

Single atomically thick graphene, with unique structural flexibility, surface sensitivity, and effective light-mater interaction, has shown exceptional advances in optoelectronics. It opens a door for diverse functionalized photonic devices, ranging from passive polarizers to active lasers and parametric oscillators. Among them, graphene-fiber biochemical sensors combine the merits of both graphene and fiber structures, demonstrating impressively high performances, such as single-molecule detectability and fast responsibility. These graphene-fiber biochemical sensors can offer tools in various applications, such as gas tracing, chemical analysis, and medical testing. In this paper, we review the emerging graphene-fiber biochemical sensors comprehensively, including the sensing principles, device fabrications, systematic implementations, and advanced applications. Finally, we summarize the state-of-the-art graphene-fiber biochemical sensors and put forward our outlooks on the development in the future. [ABSTRACT FROM AUTHOR]

Wireless monitoring of the physio-biochemical information is becoming increasingly important for healthcare. In this work, we present a proof-of-concept hydrogel-based wireless biochemical sensing scheme utilizing ultrasound. The sensing system utilizes silica-nanoparticle embedded hydrogel deposited on a thin glass substrate, which presents two prominent interfaces for ultrasonic backscattering (tissue/glass and hydrogel/glass). To overcome the effect of the varying acoustic properties of the intervening biological tissues between the sensor and the external transducer, we implemented a differential mode of ultrasonic back-scattering. Here, we demonstrate a wireless pH measurement with a resolution of 0.2 pH level change and a wireless sensing range around 10 cm in a water tank.

Recent advances in surface plasmon sensors have significantly reduced the limitations of conventional optical sensors. With the recent development of micro- and nano-fabrication technology, miniaturized one-dimensional structures become a promising platform for surface plasmon sensors for its compactness and simple structure. In this review, we describe the generation of surface plasmon polaritons and the resonance conditions. Then we categorize surface plasmon sensors by the physical quantities they detect, elaborating their working principle, performance, and current development. Finally, we summarize both limitations and advances of various design methods to provide an outlook on future directions of this field.

Surface plasmon resonance (SPR) sensor based on reflectivity measurement has been widely studied for its convenient detection, high sensitivity, and real-time functions. However, the resonance curves of SPR reflectivity spectrum are broad that lead to a low detection limit (DL) and low detection resolution. In this work, Fano resonance (FR), which has an asymmetrical sharp and narrow resonance peak, is demonstrated here to improve the DL and resolution of the plasmonic sensor. More importantly, a three-point method is employed here to analyzed and extract the polarization information of the reflected light by replacing the conventional intensity interrogation method. The sharp signal change of the Fano resonance realized by the designed configuration together with the three-point method led to a significantly enhancement on the DL and the resolution of the FR-based sensor up to one order of magnitude comparing to conventional scheme commonly used with the commercial products. Thus, the proposed sensor is of great potential for biochemical sensing such as DNA detection in terms of measuring the refractive index change at the sensing interface. [ABSTRACT FROM AUTHOR]

[Display omitted] • Plasmonic substrates for biochemical applications of SERS are reviewed. • Selected SERS biochemical analyses are briefly discussed. • SERS is one of the most sensitive analytical methods used for biochemical analysis. Due to its great practical importance, the detection and determination of many biomolecules in body fluids and other samples is carried out in a large number of laboratories around the world. One of the most promising analytical techniques now being widely introduced into medical analysis is surface-enhanced Raman scattering (SERS) spectroscopy. SERS is one of the most sensitive analytical methods, and in some cases, a good quality SERS spectrum dominated by the contribution of even a single molecule can be obtained. Highly sensitive SERS measurements can only be carried out on substrates generating a very high SERS enhancement factor and a low Raman spectral background, and so using of right nanomaterials is a key element in the success of SERS biochemical analysis. In this review article, we present progress that has been made in the preparation of nanomaterials used in SERS spectroscopy for detecting various kinds of biomolecules. We describe four groups of nanomaterials used in such measurements: nanoparticles of plasmonic metals and deposits of plasmonic nanoparticles on macroscopic substrates, nanocomposites containing plasmonic and non-plasmonic parts, nanostructured macroscopic plasmonic metals, and nanostructured macroscopic non-plasmonic materials covered by plasmonic films. We also describe selected SERS biochemical analyses that utilize the nanomaterials presented. We hope that this review will be useful for researchers starting work in this fascinating field of ​​science and technology. [ABSTRACT FROM AUTHOR]

Cu0(core)-Au0(shell) (Cu@Au) bimetallic nanoparticles (NPs) synthesized under microwave-assisted heating were interrogated for surface enhanced Raman scattering (SERS)-active substrates. NPs characterization, by XRD, XPS and UV/vis spectroscopy, showed the formation of self-assembled particles with the occurrence of electron transfer from Cu to Au and the absence of Cu x O. TEM and AF4 demonstrated NPs with a mean diameter of 4.7 nm. Despite the low LSPR shown by small nanoparticles (<10 nm diameter), our Cu@Au NPs showed enhanced SERS effect, demonstrated by the calculated scattering signal enhancement factor (3 × 105), which may be related to electromagnetic coupling. Selected examples of analytes of interest, including some biomolecules, were studied to demonstrate the versatility of our Cu@Au NPs as SERS-active substrates. Image 1 • CuAu nanostructured materials were synthesized via microwave-assisted heating. • One-step synthesis without the need of templates lead to core-shell structure. • Cu@Au nanoparticles showed enhanced SERS effect. [ABSTRACT FROM AUTHOR]

Nanochannel typically serves as a passageway of ionic current, which can offer a rapid and highly sensitive output for biochemical sensing. Solid-state nanopores/channels, by virtue of their superior mechanical and chemical stability, well-adjustable structure, and easily tailorable surface properties, draw great attention in practical nanochannel-based sensor devices. Particularly, when functioned by diverse probes, solid-state nanochannel-based sensors present specific recognition for multiple target, including ion, small molecule, nucleic acid, protein and so on. In view of this, we summarize the recent advances in the solid-state nanochannel-based biochemical sensors, classified by targets including ions, small molecules, proteins and nucleic acids. The sensing principles are firstly introduced. Then, the discussion mainly focusses on the different strategies to achieve target detection according to the interaction between targets and functional probes. In the end, some critical challenges about the future development of the functional solid-state nanochannel-based biochemical sensors are briefly proposed. • Solid-state nanopores/channels offer a rapid and sensitive ionic signal for biochemical sensing. • Nanopores/channels functionalized by probes present specific recognition for multiple targets. • Strategies of functional nanopores/channels divide into covalent and noncovalent recognitions. • Current analytes in nanochannels/pores includes ion, small molecule, protein, nucleic acid. [ABSTRACT FROM AUTHOR]

Photonic integrated circuits (PICs), the optical counterpart of traditional electronic integrated circuits, are paving the way toward truly portable and highly accurate biochemical sensors for Department of Defense (DoD)-relevant applications. We introduce the fundamentals of PIC-based biochemical sensing and describe common PIC sensor architectures developed to-date for single-identification and spectroscopic sensor classes. We discuss DoD investments in PIC research and summarize current challenges. We also provide future research directions likely required to realize widespread application of PIC-based biochemical sensors. These research directions include materials research to optimize sensor components for multiplexed sensing; engineering improvements to enhance the practicality of PIC-based devices for field use; and the use of synthetic biology techniques to design new selective receptors for chemical and biological agents. [ABSTRACT FROM AUTHOR]

A sickle-shaped metamaterial (SSM) based biochemical sensor with multiple resonances was investigated in the terahertz frequency range. The electromagnetic responses of SSM were found to be four resonances, namely dipolar, quadrupolar, octupolar and hexadecapolar plasmon resonances. They were generated from the interactions between SSM and perpendicularly incident terahertz waves. The sensing performances of SSM-based biochemical sensors were evaluated by changing ambient environments and analyte varieties. The highest values of sensitivity and figure of merit (FOM) for SSM covered with analyte thin-films were 471 GHz/RIU (refraction index unit) and 94 RIU−1, respectively. In order to further investigate the biosensing ability of the proposed SSM device, dielectric hemispheres and microfluidic chips were adopted to imitate dry and hydrous biological specimens, respectively. The results show that the sensing abilities of SSM-based biochemical sensors could be enhanced by increasing either the number of hemispheres or the channel width of the microfluidic chip. The highest sensitivity was 405 GHz/RIU for SSM integrated with microfluidic chips. Finally, three more realistic models were simulated to imitate real sensing situations, and the corresponding highest sensitivity was 502 GHz/RIU. The proposed SSM device paves the way to possible uses in biochemical sensing applications.

Zinc-based quantum dots have been widely used in analysis detection and biomarker due to their unique optical properties, low toxicity and good biocompatibility. Based on the research progress, in this paper, the synthesis methods and functionalized modifications, as well as the application of zinc-based quantum dots in the field of biochemical sensing were systematically described. The development trends and prospects of application of zinc-based quantum dots were also discussed in detail. [ABSTRACT FROM AUTHOR]

Integrating multi-responsive polymers such as microgels onto optical fiber tips, in a controlled fashion, enables unprecedented functionalities to Lab-on-fiber optrodes. The creation of a uniform microgel monolayer with a specific coverage factor is crucial for enhancing the probes responsivity to a pre-defined target parameter. Here we report a reliable fabrication strategy, based on the dip coating technique, for the controlled realization of microgel monolayer onto unconventional substrates, such as the optical fiber tip. The latter was previously covered by a plasmonic nanostructure to make it sensitive to superficial environment changes. Microgels have been prepared using specific Poly(N-isopropylacrylamide)-based monomers that enable bulky size changes in response to both temperature and pH variations. The formation of the microgel monolayer is efficiently controlled through the selection of suitable operating pH, temperature and concentration of particle dispersions used during the dipping procedure. The effect of each parameter has been evaluated, and the validity of our procedure is confirmed by means of both morphological and optical characterizations. We demonstrate that when the coverage factor exceeds 90%, the probe responsivity to microgels swelling/collapsing is significantly improved. Our study opens new paradigms for the development of engineered microgels assisted Lab-on-Fiber probes for biochemical applications. [ABSTRACT FROM AUTHOR]

Graphene is a two-dimensional (2D) material consisting of a single sheet of sp2 hybridized carbon atoms laced in a hexagonal lattice, with potentially wide usage as a Raman enhancement substrate, also termed graphene-enhanced Raman scattering (GERS), making it ideal for sensing applications. GERS improves upon traditional surface-enhanced Raman scattering (SERS), combining its single-molecule sensitivity and spectral fingerprinting of molecules, and graphene’s simple processing and superior uniformity. This enables fast and highly sensitive detection of a wide variety of analytes. Accordingly, GERS has been investigated for a wide variety of sensing applications, including chemical- and bio-sensing. As a derivative of GERS, the use of two-dimensional materials other than graphene for Raman enhancement has emerged, which possess remarkably interesting properties and potential wider applications in combination with GERS. In this review, we first introduce various types of 2D materials, including graphene, MoS2, doped graphene, their properties, and synthesis. Then, we describe the principles of GERS and comprehensively explain how the GERS enhancement factors are influenced by molecular and 2D material properties. In the last section, we discuss the application of GERS in chemical- and bio-sensing, and the prospects of such a novel sensing method.

Surface plasmon resonance (SPR) optical fiber sensors can be used as a cost-effective and relatively simple-to-implement alternative to well established bulky prism configurations for in situ high sensitivity biochemical and electrochemical measurements. The miniaturized size and remote operation ability offer them a multitude of opportunities for single-point sensing in hard-to-reach spaces, even possibly in vivo . Grating-assisted and polarization control are two key properties of fiber-optic SPR sensors to achieve unprecedented sensitivities and limits of detection. The biosensor configuration presented here utilizes a nanoscale metal-coated tilted fiber Bragg grating (TFBG) imprinted in a commercial single-mode fiber core with no structural modifications. Such sensor provides an additional resonant mechanism of high-density narrow cladding mode spectral combs that overlap with the broader absorption of the surface plasmon for high accuracy interrogation. In this paper, we briefly review the principle, characterization and implementation of plasmonic TFBG sensors, followed by our recent developments of the “surface” and “localized” affinity studies of the biomolecules for real life problems and the electrochemical actives of electroactive biofilms for clean energy resources. [ABSTRACT FROM PUBLISHER]

Wireless, passive, low-cost and portable detection systems are in high demand for environment monitoring, food safety and health care diagnosis. Among them smartphone-based sensing systems are receiving special attention with the worldwide popularity of smartphones. Over the past decade, many devices, including a large number of smartphones in today’s marketplace, are integrated with near field communication (NFC) modules. Leveraging the worldwide ubiquity of these devices, we developed wireless and passive NFC tag sensors based on flexible and low-cost NFC tags for biochemical sensing. NFC-enabled smartphone was used to wirelessly power the sensors and receive the detection results through inductive coupling. By adopting rheostats in the resonant circuits of the sensors, we easily achieved accurate semi-quantitative detection of different analytes constructed sensor arrays. The results demonstrated that the tag sensors could be used to discriminate gases at part-per-million concentrations and analytes in solution such as ions and bacteria in different concentration ranges. Thus, the wireless, passive, low-cost and flexible NFC tag sensors unfolded new dimensions for biochemical sensing with smartphones. [ABSTRACT FROM AUTHOR]

In this study, CuCl2 nanoparticles (NPs) synthesised via pulsed laser ablation in liquid (PLAL) were successfully employed to simultaneously detect glutamine and ammonia, with a limit of detection of 20 nM and up to 1500 ppm, respectively. These NPs hold potential for non-invasive diagnosis and monitoring of various health conditions using urine and sweat samples. The sensing mechanism relied on the plasmon peaks of CuCl 2 NPs in the UV range (at 300, 363, and 423 nm), which were used to correlate the levels of glutamine and ammonia concentration with the absorbance. Quasi-spherical CuO and pyramidal CuCl 2 NPs were synthesised through laser ablation of Cu powder in liquid IPA and IPA-HCl, respectively. CuCl 2 NPs displayed higher ablation efficiency, higher optical absorbance (20-fold), and an 8400-fold increase in colloidal conductivity (0.0005 vs 4.2 mS/cm) compared to CuO NPs. The NP size distribution ranged broadly from 10 nm to less than 100 nm. XPS analysis revealed that ablation in pure IPA resulted in oxidized Cu NPs, while ablation in IPA-HCl liquid medium (12 nM HCl) led to the formation of a combination of metallic copper and CuCl 2 NPs that were more conductive and had higher optical absorbance than their oxidized counterparts. [Display omitted] • Cu NPs were used as glutamine and ammonia sensors via photometry. • MetaLlic Cu and CuCl 2 nanoparticles were fabricated via laser ablation in IPA-HCl. • NP oxidation can be controlled/eliminated during PLAL by varying the liquid medium composition. [ABSTRACT FROM AUTHOR]

Light manipulation has always been the fundamental subject in the field of optics since centuries ago. Traditional optical devices are usually designed using glasses and other materials, such as semiconductors and metals. Optofluidics is the combination of microfluidics and optics, which brings a host of new advantages to conventional solid systems. The capabilities of light manipulation and biochemical sensing are inherent alongside the emergence of optofluidics. This new research area promotes advancements in optics, biology, and chemistry. The development of fast, accurate, low-cost, and small-sized biochemical micro-sensors is an urgent demand for real-time monitoring. However, the fluid flow in the on-chip sensor is usually non-uniformed, which is a new and emerging challenge for the accuracy of optical detection. It is significant to reveal the principle of light propagation in an inhomogeneous liquid flow and the interaction between biochemical samples and light in flowing liquids. In this review, we summarize the current state of optofluidic lab-on-a-chip techniques from the perspective of light modulation by the unique dynamic properties of fluid in heterogeneous media, such as diffusion, heat transfer, and centrifugation etc. Furthermore, this review introduces several novel photonic phenomena in an inhomogeneous liquid flow and demonstrates their application in biochemical sensing.

Integrating multi-responsive polymers such as microgels onto optical fiber tips, in a controlled fashion, enables unprecedented functionalities to Lab-on-fiber optrodes. The creation of a uniform microgel monolayer with a specific coverage factor is crucial for enhancing the probes responsivity to a pre-defined target parameter. Here we report a reliable fabrication strategy, based on the dip coating technique, for the controlled realization of microgel monolayer onto unconventional substrates, such as the optical fiber tip. The latter was previously covered by a plasmonic nanostructure to make it sensitive to superficial environment changes. Microgels have been prepared using specific Poly(N-isopropylacrylamide)-based monomers that enable bulky size changes in response to both temperature and pH variations. The formation of the microgel monolayer is efficiently controlled through the selection of suitable operating pH, temperature and concentration of particle dispersions used during the dipping procedure. The effect of each parameter has been evaluated, and the validity of our procedure is confirmed by means of both morphological and optical characterizations. We demonstrate that when the coverage factor exceeds 90%, the probe responsivity to microgels swelling/collapsing is significantly improved. Our study opens new paradigms for the development of engineered microgels assisted Lab-on-Fiber probes for biochemical applications.

The tilted fiber Bragg grating (TFBG) is a new kind of fiber-optic sensor that possesses all the advantages of well-established Bragg grating technology in addition to being able to excite cladding modes resonantly. This device opens up a multitude of opportunities for single-point sensing in hard-to-reach spaces with very controllable cross-sensitivities, absolute and relative measurements of various parameters, and an extreme sensitivity to materials external to the fiber without requiring the fiber to be etched or tapered. Over the past five years, our research group has been developing multimodal fiber-optic sensors based on TFBG in various shapes and forms, always keeping the device itself simple to fabricate and compatible with low-cost manufacturing. This paper presents a brief review of the principle, fabrication, characterization, and implementation of TFBGs, followed by our progress in TFBG sensors for mechanical and biochemical applications, including one-dimensional TFBG vibroscopes, accelerometers and micro-displacement sensors; two-dimensional TFBG vector vibroscopes and vector rotation sensors; reflective TFBG refractometers with in-fiber and fiber-to-fiber configurations; polarimetric and plasmonic TFBG biochemical sensors for in-situ detection of cell, protein and glucose. [ABSTRACT FROM AUTHOR]