Non-invasive Medical Diagnosis Research Articles

A Wireless Wearable Sensor System Based on a Silver Nanowire‐Decorated Silicon Nanomembrane for Precise and Continuous Hazardous Gas Monitoring

AbstractWearable wireless gas sensors have attracted enormous interest due to precise, real‐time healthcare and environmental monitoring without temporal and spatial limitations. Among various toxic gases, detecting ammonia is crucial because of its highly hazardous nature and applicability as a noninvasive biomarker for diagnosing health conditions. In this study, silver nanowires‐decorated silicon nanomembrane (AgNW‐SiNM) chemiresistive gas sensor with high selectivity to ammonia is fully integrated with an ultrathin flexible Joule heater and wireless communication system to fabricate wearable wireless real‐time toxic gas monitoring system. The sensor exhibits improved performance to ammonia gas, attributed to heating‐induced changes in adsorption/desorption rates, along with electronic and chemical sensitization facilitated by AgNW decoration. The gas sensing system exhibits stable and high responses of ≈1.83, 1.47, and 1.19 on the ammonia exposure at concentrations of 10, 5, and 1 ppm even under mechanical deformations. The real‐time dynamic response of the sensor is wirelessly transmitted to portable electronics and displayed on the screen. Moreover, the system alerts the users in advance through the integrated haptic interface when exposed to dangerous gas environments for early evacuation. The system paves the way for timely warnings from hazardous gas and more accurate noninvasive medical diagnosis related to respiratory disorders.

(Invited) Metal Oxide Nanowire Array to Overcome Odor Sensing Limits

Toward developing advanced cyber-physical system (CPS), interest for a molecular recognition electronics is rapidly increasing for collecting chemical information in our daily life. Among various sensor technology, artificial olfactory sensor targeting on chemical data collection of odor is growing research field due to its promise in wide applications for non-invasive medical diagnosis, environmental monitoring, factory automation, security, smart agriculture, etc. In such applications, a lack of molecular sensing system having both material robustness and capability of molecular discrimination in complex mixtures has been a critical issue for the long-term collection of chemical information. Inorganic nanowires, especially for metal oxide nanowires, are a class of promising materials to overcome such issues due to their excellent material robustness in air and huge surface-to-volume ratio beneficial for effectively capturing and concentrating volatile molecules on their surface. Although a highly sensitive electrical detection of volatile molecules has been demonstrated using semiconducting nanowires up to date, poor understanding and design capability of molecule-to-surface interactions on nanowire surface have substantially limited their performance in artificial olfactory sensor systems which require molecular discrimination in complex mixtures.In this presentation, we demonstrate that designing a coordination structure of ionic species at nanowire surface is of critical importance to control the adsorption, reaction and desorption properties of volatile molecules. The enhanced sensing performance and the molecular selective adsorption property of nanowire were successfully achieved as the results of designed surface coordination structure. In addition, molecular filter/molecular transport controller using nanowire array integrated with sensor device is conceptualized as novel artificial olfactory sensor system to discriminate molecules in complex mixture beyond the previous sensing limits.

Robust Sample Information Retrieval in Dark-Field Computed Tomography With a Vibrating Talbot-Lau Interferometer.

X-ray computed tomography (CT) is a crucial tool for non-invasive medical diagnosis that uses differences in materials' attenuation coefficients to generate contrast and provide 3D information. Grating-based dark-field-contrast X-ray imaging is an innovative technique that utilizes small-angle scattering to generate additional co-registered images with additional microstructural information. While it is already possible to perform human chest dark-field radiography, it is assumed that its diagnostic value increases when performed in a tomographic setup. However, the susceptibility of Talbot-Lau interferometers to mechanical vibrations coupled with a need to minimize data acquisition times has hindered its application in clinical routines and the combination of X-ray dark-field imaging and large field-of-view (FOV) tomography in the past. In this work, we propose a processing pipeline to address this issue in a human-sized clinical dark-field CT prototype. We present the corrective measures that are applied in the employed processing and reconstruction algorithms to mitigate the effects of vibrations and deformations of the interferometer gratings. This is achieved by identifying spatially and temporally variable vibrations in air reference scans. By translating the found correlations to the sample scan, we can identify and mitigate relevant fluctuation modes for scans with arbitrary sample sizes. This approach effectively eliminates the requirement for sample-free detector area, while still distinctly separating fluctuation and sample information. As a result, samples of arbitrary dimensions can be reconstructed without being affected by vibration artifacts. To demonstrate the viability of the technique for human-scale objects, we present reconstructions of an anthropomorphic thorax phantom.

An energy transfer strategy towards versatile sensing applications from Cr3+ and Yb3+ codoped near infrared phosphors

Near-infrared (NIR) phosphors have garnered notable attention for their extensive applications in anti-counterfeiting, optical imaging, non-invasive medical diagnosis and detection. Nevertheless, the quest for NIR phosphors with outstanding detection and sensing capabilities remains a challenge. In this study, we have successfully prepared Ga1.6Mg0.2Ge0.2O3:Cr3+,Yb3+ NIR phosphors by codoping and substitutation strategies. When incorporated into polydimethylsiloxane films, these phosphors demonstrated a direct correlation between luminescence intensity ratio and applied stress under 450 nm excitation. Moreover, variations in luminescence spectra occurred with different compositions and concentrations of liquids coated on the film, facilitating both force measurement and composition analysis. Furthermore, a NIR phosphor-converted light-emitting diode (pc-LED) was fabricated by integrating phosphor with a blue LED chip, exhibiting excellent performance. Utilizing the prepared NIR pc-LED as a light source, we facilitated non-destructive imaging, night vision, and anti-counterfeiting applications with an infrared camera. These findings suggest that the synthesized NIR phosphors possess hold promise for diverse detection and sensing applications.

Modular Construction of Vinylene-Linked Covalent Organic Frameworks with Tunable Emission for Tumor Visualization.

Covalent organic frameworks (COFs) with ordered π structures are very promising in porous light-emitting materials. However, most of these COFs are either poor in luminescence or lack of water-stability. Herein, a series of isostructural D-A vinylene-linked COFs were constructed based a new D2h symmetric linker 1,4-bis(4,6-dimethyl-1,3,5-triazin-2-yl)benzene (TMTA) with high crystallinity, comparative high surface area and excellent chemical/thermal stability. Impressively, their adsorption and luminescence wavelength vary with respect to the density of π-systems in the electron-donating group, which constitute the foundation for molecular engineering the luminescent properties of vinylene-linked COFs. The DFT calculations further established the relationship between the luminescence properties and the donor electronic structure. Moreover, one of representative COF named FZU-203 showed inspiring applications in bioimaging, which may further provide strategic guidance for the use of vinylene-linked COFs as fluorescent nanoprobes in non-invasive medical diagnosis and visualization therapy of tumors.

Strategy of Charge Compensation for High-Performance Ni2+-Activated MgAl2O4 Spinel Near-Infrared Phosphor Synthesis via the Sol-Gel Combustion Method.

Near-infrared (NIR) phosphor conversion light-emitting diodes (pc-LEDs) have great application potential as NIR light sources in many fields such as food analysis, night vision illumination, and bioimaging for noninvasive medical diagnosis. In general, phosphors synthesized by a high-temperature solid-phase method have large particle sizes and have to be processed to fine powders by a grinding process, which may introduce surface defects and lower the luminous efficiency. Here, we report a sol-gel sintering method with ammonium nitrate and citric acid as the sacrificing agents to synthesize high purity, nanosized (less than 50 nm) Zr4+/Ni2+ codoped MgAl2O4 spinel NIR phosphors, in which MgAl2O4 spinel is the matrix, Ni2+ is the luminous center, and Zr4+ acts as the charge compensator. We systematically characterized the crystal structures and NIR luminescence properties of the Ni2+-doped MgAl2O4 and the Zr4+/Ni2+ codoped MgAl2O4. Under 390 nm light excitation, the emission spectrum of the Ni2+-doped MgAl2O4 phosphor covers 900-1600 nm, the half-peak width is 251 nm, and the peak position is located at 1230 nm. We demonstrated that by incorporating small amounts of Zr4+ as the charge compensator, the NIR emission intensity of the Zr4+/Ni2+ codoped MgAl2O4 nanosized phosphor was doubled over that of the Ni2+-doped MgAl2O4 phosphor. The optimal content of the charge compensator was 2 mol %. More importantly, the inclusion of Zr4+ led to a NIR phosphor with improved thermal stability in luminous properties, and the luminous intensity measured at 100 °C was 33.83% of that measured at room temperature (20 °C). This study demonstrates that NIR phosphor nanomaterials with high-purity and enhanced optical properties can be designed and synthesized through the charge compensation strategy by a sol-gel sintering method.

Electrochemical Nonenzymatic Acetone Sensing: A Novel Approach of Biosensor Platform Based on CNT/CuO Nanosystems

AbstractA promising approach for noninvasive medical diagnosis may be to measure the VOCs produced by metabolic changes or pathological disorders in human sweat, such as measuring the acetone levels in the presence of diabetes. Acetone is a by‐product of fat catabolism and serves as an indicator of ketosis and diabetes. The measurement of acetone may be used instead of glucose monitoring. Current research aims to develop and improve noninvasive methods of detecting acetone in sweat that are accurate, sensitive, and stable. The carbon nanotubes (CNTs)–copper oxide (CuO) nanocomposite (NC) improves direct electron transport to the electrode surface in this study. The complex‐precipitation method is used to make this NC. X‐ray diffraction (XRD) and scanning electron microscopy (SEM) are used to investigate the crystal structure and morphology of the prepared catalyst. Using cyclic voltammetry (CV) and amperometry, the electrocatalytic activity of the as‐prepared catalyst is evaluated. The electrocatalytic activity in artificial sweat solution is examined at various scan rates and acetone concentrations. The detection limit of the CNTs‐CuO NC catalyst is 0.05 mm, with a sensitivity of 16.1 mA cm−2 µm−1 in a linear range of 1–50 mm. Furthermore, this NC demonstrates a high degree of selectivity for various biocompounds found in sweat, with no interfering cross‐reactions from these species. The CNT‐CuO NC, as produced, has good sensitivity, rapid reaction time (2 s), and stability, indicating its potential for acetone sensing.

Development of a lead-free, high-frequency ultrasound transducer with broad bandwidth and enhanced pulse-echo response, employing β-Ni(OH)2/PVDF-TrFE piezoelectric composite

Piezoelectric composite-based high-frequency ultrasound transducers (USTs) have gained significant prominence as a leading and effective tool in non-invasive medical diagnosis, non-destructive testing and diverse industrial applications. In this study, we present the fabrication of a lead-free, high-frequency ultrasound transducer (P-UST), having a very simple and unique assembly procedure. To achieve this, we employed PVDF-TrFE based piezoelectric composite thin film (NTr5) integrated with a transition metal hydroxide (β-Ni(OH)2 nanoplates) and demonstrated its outstanding performance, thereby showcasing its potential in various applications. The composite exhibited exceptional β-phase crystallization, reaching impressive maximum value of 90.04%, owing to the favorable interaction between electrostatic ions and dipoles, along with the presence of strong surface polarization. Upon analysis, remarkable piezoelectric (d33∼50.22 pm/V) and ferroelectric properties were observed in the composite material, accompanied by significant enhancement in surface roughness. Here, the piezoelectric property's impact on UST output is well-explained using Maxwell's equation. P-UST, being a versatile system, is capable of generating and receiving pulse signals. By conducting a pulse-echo test on an aluminium block with ultrasound gel, we achieved a peak-to-peak output voltage of 5.19 V, surpassing the output voltage magnitude of any previously reported UST in this field. The Fast Fourier transformed data of the voltage output revealed an impressive −6 dB bandwidth of 51.22 MHz (102.4%) with a high central frequency of 50.01 MHz. Hence, our P-UST's exceptionally high central frequency promises significantly enhanced ultrasound image resolution, which expands the potential for highly accurate medical assessments for advanced healthcare outcomes and improving patient well-being.

Application of serum SERS technology combined with deep learning algorithm in the rapid diagnosis of immune diseases and chronic kidney disease

Surface-enhanced Raman spectroscopy (SERS), as a rapid, non-invasive and reliable spectroscopic detection technique, has promising applications in disease screening and diagnosis. In this paper, an annealed silver nanoparticles/porous silicon Bragg reflector (AgNPs/PSB) composite SERS substrate with high sensitivity and strong stability was prepared by immersion plating and heat treatment using porous silicon Bragg reflector (PSB) as the substrate. The substrate combines the five deep learning algorithms of the improved AlexNet, ResNet, SqueezeNet, temporal convolutional network (TCN) and multiscale fusion convolutional neural network (MCNN). We constructed rapid screening models for patients with primary Sjögren’s syndrome (pSS) and healthy controls (HC), diabetic nephropathy patients (DN) and healthy controls (HC), respectively. The results showed that the annealed AgNPs/PSB composite SERS substrates performed well in diagnosing. Among them, the MCNN model had the best classification effect in the two groups of experiments, with an accuracy rate of 94.7% and 92.0%, respectively. Previous studies have indicated that the AgNPs/PSB composite SERS substrate, combined with machine learning algorithms, has achieved promising classification results in disease diagnosis. This study shows that SERS technology based on annealed AgNPs/PSB composite substrate combined with deep learning algorithm has a greater developmental prospect and research value in the early identification and screening of immune diseases and chronic kidney disease, providing reference ideas for non-invasive and rapid clinical medical diagnosis of patients.

Highly Strain-Stable Intrinsically Stretchable Olfactory Sensors for Imperceptible Health Monitoring.

Intrinsically stretchable gas sensors possess outstanding advantages in seamless conformability and high-comfort wearability for real-time detection toward skin/respiration gases, making them promising candidates for health monitoring and non-invasive disease diagnosis and therapy. However, the strain-induced deformation of the sensitive semiconductor layers possibly causes the sensing signal drift, resulting in failure in achievement of the reliable gas detection. Herein, a surprising result that the stretchable organic polymers present a universal strain-insensitive gas sensing property is shown. All the stretchable polymers with different degrees of crystallinity, including indacenodithiophene-benzothiadiazole (PIDTBT), diketo-pyrrolo-pyrrole bithiophene thienothiophene (DPPT-TT) and poly[4-(4,4-dihexadecyl-4H-cyclopenta[1,2-b:5,4-b']dithiophen-2-yl)-alt-[1,2,5]thiad-iazolo [3,4-c] pyridine] (PCDTPT), show almost unchanged gas response signals in the different stretching states. This outstanding advantage enables the intrinsically stretchable devices to imperceptibly adhere on human skin and well conform to the versatile deformations such as bending, twisting, and stretching, with the highly strain-stable gas sensing property. The intrinsically stretchable PIDTBT sensor also demonstrates the excellent selectivity toward the skin-emitted trimethylamine (TMA) gas, with a theoretical limit of detection as low as 0.3ppb. The work provides new insights into the preparation of the reliable skin-like gas sensors and highlights the potential applications in the real-time detection of skin gas and respiration gas for non-invasive medical treatment and disease diagnosis.

PbS QD-Coated Si Micro-Hole Array/Graphene vdW Schottky Near-Infrared Photodiode for PPG Heart Rate Measurement.

Near-infrared (NIR) photodetectors (PDs) have attracted much attention for use in noninvasive medical diagnosis and treatments. In particular, self-filtered NIR PDs are in high demand for a wide range of biomedical applications due to their ability for wavelength discrimination. In this work, we designed and then fabricated a Si micro-hole array/Graphene (Si MHA/Gr) van der Waals (vdW) Schottky NIR photodiode using a PbS quantum dot (QD) coating. The device exhibited a unique self-filtered NIR response with a responsivity of 0.7 A/W at -1 V and a response speed of 61 μs, which is higher than that seen without PbS QD coating and even in most previous Si/Gr Schottky photodiodes. The light trapping of the Si MHA and the PbS QD coating could be attributed to the high responsivity of the vdW photodiode. Furthermore, the presented NIR photodiode could also be integrated in photoplethysmography (PPG) for real-time heart rate (HR) monitoring. The extracted HR was in good accord with the values measured with the patient monitor-determined by analyzing the Fourier transform of the stable and reliable fingertip PPG waveform-suggesting its potential for practical applications.

Dual-response drug released hollow materials for the ultrasonic theranostics of acute myocardial infarction

Acute myocardial infarction (AMI) is a type of serious heart attack. Timely diagnosis and treatment of patients greatly improved their survival and prognosis. Unfortunately, during the progression of AMI, some diagnostic markers, including ST-segment elevation on electrocardiograph and serum troponin, sometimes cannot be obtained changing at an early stage. In addition, the imaging methods such as CT cannot dynamically monitor the AMI. Ultrasound (US) imaging can be considered as a convenient and non-invasive medical diagnosis modality in clinical. But it lacks the targeted ultrasound contrast agent for the diagnosis of AMI. High expression of MMP-9 and ROS was found to be happened with AMI. However, a single targeting of one between them could be interfered by other factors. Here, we successfully synthesized the hollow organic material combining the polymerization of MMP-9 substrate polypeptide and ROS responsive organic compounds in order to have more accuracy targeting to AMI. Dimethyldiethoxysilane (DMDES) was used to achieve colloidal stabilized oil-in-water emulsion template. Thus, the polypeptide and ROS-responsive compound, which have the opposite polarity, can be dissolved in water and oil species, respectively, and react on the surface of these two phases. Moreover, the curcumin (CUR) was also loaded into the hollow material for the targeted release, which realized the theranostics. This material was confirmed with uniform particle size, hollow mesopores, biosafety and ultrasonic imaging enhancement ability both in vitro and in vivo. Furthermore, this material was also demonstrated to have MMP-9 and ROS targeting imaging enhancement and drug releasement both in vitro and in vivo, as well as good therapeutic effects on AMI model cells or mice.

Modeling vibrations of a tiled Talbot-Lau interferometer on a clinical CT.

X-ray computed tomography (CT) is an invaluable imaging technique for non-invasive medical diagnosis. However, for soft tissue in the human body the difference in attenuation is inherently small. Grating-based X-ray phase-contrast is a relatively novel imaging method which detects additional interaction mechanisms between photons and matter, namely refraction and small-angle scattering, to generate additional images with different contrast. The experimental setup involves a Talbot-Lau interferometer whose susceptibility to mechanical vibrations hindered acquisition schemes suitable for clinical routine in the past. We present a processing pipeline to identify spatially and temporally variable fluctuations occurring in an interferometer installed on a continuously rotating clinical CT gantry. The correlations of the vibrations in the modular grating setup are exploited to identify a small number of relevant fluctuation modes, allowing for a sample reconstruction free of vibration artifacts.

Metal Oxide Gas Sensors to Study Acetone Detection Considering Their Potential in the Diagnosis of Diabetes: A Review.

Metal oxide (MOx) gas sensors have attracted considerable attention from both scientific and practical standpoints. Due to their promising characteristics for detecting toxic gases and volatile organic compounds (VOCs) compared with conventional techniques, these devices are expected to play a key role in home and public security, environmental monitoring, chemical quality control, and medicine in the near future. VOCs (e.g., acetone) are blood-borne and found in exhaled human breath as a result of certain diseases or metabolic disorders. Their measurement is considered a promising tool for noninvasive medical diagnosis, for example in diabetic patients. The conventional method for the detection of acetone vapors as a potential biomarker is based on spectrometry. However, the development of MOx-type sensors has made them increasingly attractive from a medical point of view. The objectives of this review are to assess the state of the art of the main MOx-type sensors in the detection of acetone vapors to propose future perspectives and directions that should be carried out to implement this type of sensor in the field of medicine.

Machine learning identification of atmospheric gases by mapping the graphene-molecule van der waals complex bonding evolution

Atmospheric doping of graphene, and the variation in atmospheric composition (e.g., humidity) makes graphene machine learning (ML) models limited to controlled environments (e.g., dry air), and unsuitable for atmospheric applications (e.g., non-invasive medical diagnosis). Herein, using nano-porous activated carbon for atmospheric passivation of the graphene channel, Extreme Gradient Boosting (XGBoost), K-nearest neighbors (KNN), and Naïve Bayes supervised ML models for atmospheric gas identification were developed, with model feature contribution studied using the Game theoretic approach, SHapley Additive exPlanations (SHAP). Unlike conventional graphene-based ML models which only monitor the gas adsorption induced doping and scattering without tuning voltage (Vt) modulation, in this work, the tuning voltage evolution of the gas adsorption induced van der Waals (vdW) complex doping and scattering characteristics was mapped out over time. The accuracy, precision, recall, and F1-score of the developed models in the environments: atmospheric ammonia, atmospheric acetone, ammonia in dry air, and acetone in nitrogen were 100% for XGBoost, 96%, 97%, 97%, 97% respectively for KNN, and 95%, 95%, 96%, 96% respectively for Naïve Bayes, even at single-digit ppb gas concentrations. Hence, our results advance the application of graphene based electronic nose models from conventional controlled environments to actual atmospheric sensing.

Surface-enhanced Raman scattering as a potential strategy for wearable flexible sensing and point-of-care testing non-invasive medical diagnosis.

As a powerful and effective analytical tool, surface-enhanced Raman scattering (SERS) has attracted considerable research interest in the fields of wearable flexible sensing and non-invasive point-of-care testing (POCT) medical diagnosis. In this mini-review, we briefly summarize the design strategy, the development progress of wearable SERS sensors and its applications in this field. We present SERS substrate analysis of material design requirements for wearable sensors and highlight the benefits of novel plasmonic particle-in-cavity (PIC)-based nanostructures for flexible SERS sensors, as well as the unique interfacial adhesion effect and excellent mechanical properties of natural silk fibroin (SF) derived from natural cocoons, indicating promising futures for applications in the field of flexible electronic, optical, and electrical sensors. Additionally, SERS wearable sensors have shown great potential in the fields of different disease markers as well as in the diagnosis testing for COVID-19. Finally, the current challenges in this field are pointed out, as well as the promising prospects of combining SERS wearable sensors with other portable health monitoring systems for POCT medical diagnosis in the future.

Porous Oxide-Functionalized Seaweed Fabric as a Flexible Breath Sensor for Noninvasive Nephropathy Diagnosis.

Ever-increasing quality of life demands low-power and reliable gas-sensing technology for point-of-care monitoring of human health by relevant breath biomarkers. However, precise identification is rather challenging due to the relatively small concentration and an abundance of interferents. Herein, a breath sensor that can detect ppb-level ammonia is constructed based on a soft-hard interface design of biocompatible seaweed fabric and nanosheet-assembled bismuth oxide architectures after undergoing heat treatment. Benefiting from abundant defective sites and surface chemical state changes, the flexible sensor can work at room temperature and exhibits superior characteristics for ammonia detection, including ultrahigh response (1296), short response/recovery time (12/6 s), small detection limit (117 ppb), and remarkable anti-interference, even after repetitive mechanical bending and long-term fatigue. Furthermore, the flexible sensor demonstrates a noticeable response to the exhaled breath of a patient with Helicobacter pylori infection. After connecting the sensor with a green-light-emitting diode (LED) in the circuit, an alarm system successfully warns about ammonia levels based on the brightness of the LED. This work provides a potential strategy for wide-range ammonia detection and opens new applications in predictive and personalized healthcare platforms for noninvasive medical diagnosis.

Highly Sensitive Refractive Index Sensor Based on Polymer Bragg Grating: A Case Study on Extracellular Vesicles Detection.

The measurement of small changes in the refractive index (RI) leads to a comprehensive analysis of different biochemical substances, paving the way to non-invasive and cost-effective medical diagnosis. In recent times, the liquid biopsy for cancer detection via extracellular vesicles (EV) in the bodily fluid is becoming very popular thanks to less invasiveness and stability. In this context, here we propose a highly sensitive RI sensor based on a compact high-index-coated polymer waveguide Bragg grating with a metal under cladding. Owing to the combined effect of a metal under cladding and a high-index coating, a significant enhancement in the RI sensitivity as well as the dynamic range has been observed. The proposed sensor has been analyzed by combining finite element method (FEM) and coupled-mode theory (CMT) approaches, demonstrating a sensitivity of 408–861 nm/RIU over a broad dynamic range of 1.32–1.44, and a strong evanescent field within a 150 nm proximity to the waveguide surface compliant with EV size. The aforementioned performance makes the proposed device suitable for performing real-time and on-chip diagnoses of cancer in the early stage.

An Overview on the Application of Solid Phase Microextraction in the Analysis of Volatile Organic Compounds as Potential Biomarkers of Cancer

The search for biomarkers of diseases, especially for the early detection of cancer, is one of the most popular research fields in biomedicine. The development of non-invasive screening techniques for the early detection of cancer is one of the greatest scientific challenges of the 21st century. Because various diseases cause to generation of biomarkers in the body, early diagnosis of diseases can be performed by analyzing these biomarkers in all body feces. Detection of volatile organic compounds (VOCs) as biomarkers of the body's metabolic processes is a new frontier in the fast, sensitive, selective and non-invasive analysis and medical diagnosis of human diseases. VOCs as biomarkers in the human body can be distinct and specific to metabolic conditions or diseases. VOCs produced as end products of cellular metabolism and are released through a variety of biological matrices such as breath, blood, saliva, urine and feces. The study of volatile metabolites in the body fluids of the patients is performed to establish "potential biomarkers" for early diagnosis and prognosis of the disease. Various genetic, epigenetic, proteomic, and metabolic markers are evaluated for early detection of cancer. One of the promising emerging methods for early detection of cancer is the analysis of VOCs. The purpose of this review is to provide insights for recent research work on the analysis of VOC-biomarker of cancers with extraction by solid phase microextraction (SPME), and how to detect VOCs in different body matrices as a potential biomarker of disease.

Research progress on photoacoustic SF6 decomposition gas sensor in gas-insulated switchgear

In the power industry, sulfur hexafluoride (SF6) as an insulating gas is widely used in gas-insulated switchgears (GISs). Owing to the latent inner insulation defects of GIS, various SF6 gas decompositions are generated in the process of partial superheating and partial discharge (PD). The decomposition components and concentrations are different under different PD types. A number of gas sensors were reported for the detection of these decompositions. Photoacoustic spectroscopy (PAS) gas sensors have been developed for many applications owing to their high sensitivity and selectivity, such as gas pollutant detection, industrial process control, and non-invasive medical diagnosis. Due to the SF6 physical constants being different from that of nitrogen (N2) or air, the sensor structure should be redesigned. A detailed review of four different types of PAS-based gas sensors is discussed and compared.