SERS detection of surface-adsorbent toxic substances of microplastics based on gold nanoparticles and surface acoustic waves.

Microplastics adsorb toxic substances and act as a transport medium. When microplastics adsorbed with toxic substances accumulate in the body, the microplastics and the adsorbed toxic substances can cause serious diseases, such as cancer. This work aimed to develop a surface-enhanced Raman spectroscopy (SERS) detection method for surface-adsorbent toxic substances by forming gold nanogaps on microplastics using surface acoustic waves (SAWs). Polystyrene microparticles (PSMPs; 1 µm) and polycyclic aromatic hydrocarbons (PAHs), including pyrene, anthracene, and fluorene, were selected as microplastics and toxic substances, respectively. Gold nanoparticles (AuNPs; 50 nm) were used as a SERS agent. The Raman characteristic peaks of the PAHs adsorbed on the surface of PSMPs were detected, and the SERS intensity and logarithm of the concentrations of pyrene, anthracene, and fluorene showed a linear relationship (R2 = 0.98), and the limits of detection were 95, 168, and 195 nM, respectively. Each PAH was detected on the surface of PSMPs, which were adsorbed with toxic substances in a mixture of three PAHs, indicating that the technique can be used to elucidate mixtures of toxic substances. The proposed SERS detection method based on SAWs could sense toxic substances that were surface-adsorbed on microplastics and can be utilized to monitor or track pollutants in aquatic environments.

Aggregation of Ag nanoparticle based on surface acoustic wave for surface-enhanced Raman spectroscopy detection of dopamine.

BACKGROUND: Dopamine (DA), a vital neurotransmitter, plays a critical role in the human brain and relates to neuropsychiatric disorders such as Parkinson's disease and schizophrenia. Numerous studies have explored detection of such biomarkers through surface-enhanced Raman spectroscopy (SERS). However, most of the studies focused on SERS detection face significant challenges with plasmonic nanostructure development. Such challenges often include time-consuming processes, complex fabrication, specialized chemical labeling, poor reproducibility, and random hotspot generation. Therefore, the need for simple and rapid nanostructure development is evident in SERS. RESULTS: We propose an innovative SERS-active sensing technique for 50 nm silver nanoparticle (AgNP) clustering based on surface acoustic wave (SAW). When a 1 µL droplet of AgNP colloid is dispensed onto the SAW-propagation zone, the AgNP cluster is deposited after the droplet completely evaporates, developing plasmonic nanogaps for SERS hotspot caused by spherical AgNP aggregation. By optimizing the SAW system through the hydrophobic treatment and modulation of the operational power, the SAW-induced AgNP clustering showed densely packed AgNP within a dot-like configuration (∼2200 AgNP µm-2), effectively preventing particle welding. The characterization of 4-mercaptobenzoic acid as a probe analyte revealed that concentrations as low as 1.14 pM was detected using our SAW-SERS system under 785 nm laser excitation. Moreover, DA was detected up to 4.28 nM with a determination of 0.99 (R2). SIGNIFICANCE: This technique for AgNP clustering induced by SAW provides a rapid, in situ, label-free SERS sensing method with outstanding sensitivity and linearity. A mere act of dropping can create extensive plasmonic hotspots featuring nanogap of ∼1.5 nm. The SAW-induced AgNP clustering can serve as an ultrasensitive SERS-active substrate for diverse molecular detections, including neurotransmitter detection.

Conducting polymer composite-based biosensing materials for the diagnosis of lung cancer: A review.

The development of a simple and fast cancer detection method is crucial since early diagnosis is a key factor in increasing survival rates for lung cancer patients. Among several diagnosis methods, the electrochemical sensor is the most promising one due to its outstanding performance, portability, real-time analysis, robustness, amenability, and cost-effectiveness. Conducting polymer (CP) composites have been frequently used to fabricate a robust sensor device, owing to their excellent physical and electrochemical properties as well as biocompatibility with nontoxic effects on the biological system. This review brings up a brief overview of the importance of electrochemical biosensors for the early detection of lung cancer, with a detailed discussion on the design and development of CP composite materials for biosensor applications. The review covers the electrochemical sensing of numerous lung cancer markers employing composite electrodes based on the conducting polyterthiophene, poly(3,4-ethylenedioxythiophene), polyaniline, polypyrrole, molecularly imprinted polymers, and others. In addition, a hybrid of the electrochemical biosensors and other techniques was highlighted. The outlook was also briefly discussed for the development of CP composite-based electrochemical biosensors for POC diagnostic devices.

Quantitative detection of dopamine in human serum with surface-enhanced Raman scattering (SERS) of constrained vibrational mode.

Dopamine (DA) is a crucial neurotransmitter involved in the hormonal, nervous, and vascular systems being considered as an index to diagnose neurodegenerative diseases, including Parkinson's and Alzheimer's disease. Herein, we demonstrate the quantitative sensing of DA using the peak shift in surface-enhanced Raman scattering (SERS) of 4-mercaptophenylboronic acid (4-MPBA), resulting from the concentration of DA. To enable the signal enhancement of Raman scattering, Ag nanostructure was built with one-step gas-flow sputtering. 4-MPBA was then introduced using vapor-based deposition, acting as a reporter molecule for bonding with DA. The gradual peak-shift from 1075.6 cm-1 to 1084.7 cm-1 was observed with the increasing concentration of DA from 1 pM to 100nM. The numerical simulation revealed that DA bonding induced a constrained vibrational mode corresponding to 1084.7 cm-1 instead of a C-S-coupled C-ring in-plane bending mode of 4-MPBA corresponding to 1075.6 cm-1. Proposed SERS sensors depicted reliable DA detection in human serum and good selectivity against other analytes, including glucose, creatinine, and uric acid.

Machine Learning-Based Predicted Age of the Elderly on the Instrumented Timed Up and Go Test and Six-Minute Walk Test.

A decrease in dynamic balance ability (DBA) in the elderly is closely associated with aging. Various studies have investigated different methods to quantify the DBA in the elderly through DBA evaluation methods such as the timed up and go test (TUG) and the six-minute walk test (6MWT), applying the G-Walk wearable system. However, these methods have generally been difficult for the elderly to intuitively understand. The goal of this study was thus to generate a regression model based on machine learning (ML) to predict the age of the elderly as a familiar indicator. The model was based on inertial measurement unit (IMU) data as part of the DBA evaluation, and the performance of the model was comparatively analyzed with respect to age prediction based on the IMU data of the TUG test and the 6MWT. The DBA evaluation used the TUG test and the 6MWT performed by 136 elderly participants. When performing the TUG test and the 6MWT, a single IMU was attached to the second lumbar spine of the participant, and the three-dimensional linear acceleration and gyroscope data were collected. The features used in the ML-based regression model included the gait symmetry parameters and the harmonic ratio applied in quantifying the DBA, in addition to the features of description statistics for IMU signals. The feature set was differentiated between the TUG test and the 6MWT, and the performance of the regression model was comparatively analyzed based on the feature sets. The XGBoost algorithm was used to train the regression model. Comparison of the regression model performance according to the TUG test and 6MWT feature sets showed that the performance was best for the model using all features of the TUG test and the 6MWT. This indicated that the evaluation of DBA in the elderly should apply the TUG test and the 6MWT concomitantly for more accurate predictions. The findings in this study provide basic data for the development of a DBA monitoring system for the elderly.

The Validity of Wireless Earbud-Type Wearable Sensors for Head Angle Estimation and the Relationships of Head with Trunk, Pelvis, Hip, and Knee during Workouts.

The present study was performed to investigate the validity of a wireless earbud-type inertial measurement unit (Ear-IMU) sensor used to estimate head angle during four workouts. In addition, relationships between head angle obtained from the Ear-IMU sensor and the angles of other joints determined with a 3D motion analysis system were investigated. The study population consisted of 20 active volunteers. The Ear-IMU sensor measured the head angle, while a 3D motion analysis system simultaneously measured the angles of the head, trunk, pelvis, hips, and knees during workouts. Comparison with the head angle measured using the 3D motion analysis system indicated that the validity of the Ear-IMU sensor was very strong or moderate in the sagittal and frontal planes. In addition, the trunk angle in the frontal plane showed a fair correlation with the head angle determined with the Ear-IMU sensor during a single-leg squat, reverse lunge, and standing hip abduction; the correlation was poor in the sagittal plane. Our results indicated that the Ear-IMU sensor can be used to directly estimate head motion and indirectly estimate trunk motion.

Catalytic SrMoO4 nanoparticles and conducting polymer composite sensor for monitoring of K+-induced dopamine release from neuronal cells.

Octahedral SrMoO4 nanoparticles (NPs) with a high degree of crystallinity and controlled size (250-350 nm) were synthesized for the first time by employing a facile hydrothermal method. The prepared NPs were composited with a carboxyl group bearing conducting polymer (2,2:5,2-terthiophene-3-(p-benzoic acid, TBA)) to attain a stable sensor probe (pTBA/SrMoO4) which was analyzed using various surface analysis methods. The catalytic performance of the composite electrode was explored as an oxidation catalyst for biological molecules through anchoring on the conducting polymer layer, which functioned as a matrix to enhance the stability and selectivity of the sensor probe. The pTBA/SrMoO4 coated on glassy carbon displayed excellent electrocatalytic performance for the oxidation of some biologically important molecules, including dopamine (DA) in neuronal cells. The sensor immobilized with the catalyst showed an excellent response for DA with a dynamic range between 0.2 and 500 µM and a detection limit of 5 nM. The proposed sensor demonstrates the detection of trace DA released from PC12 cells under K+ stimulation, followed by inhibition of the release of exogenic DA by a Ca2+ channel blocker (nifedipine). The developed method provides an interesting way to monitor the effect of extracellular substances on living cells and the drug potency test.

Predicting Sarcopenia of Female Elderly from Physical Activity Performance Measurement Using Machine Learning Classifiers.

PURPOSE: Sarcopenia is a symptom in which muscle mass decreases due to decreasing in the number of muscle fibers and muscle cross-sectional area as aging. This study aimed to develop a machine learning classification model for predicting sarcopenia through a inertial measurement unit (IMU)-based physical performance measurement data of female elderly. PATIENTS AND METHODS: Seventy-eight female subjects from an elderly population (aged: 78.8±5.7 years) volunteered to participate in this study. To evaluate the physical performance of the elderly, the experiment conducted timed-up-and-go test (TUG) and 6-minute walk test (6mWT) with worn a single IMU. Based on literature review, 132 features were extracted from collected data. Feature selection was performed through the Kruskal-Wallis test, and features datasets were constructed according to feature selection. Three major machine learning-based classification algorithms classified the sarcopenia group in each dataset, and the performance of classification models was compared. RESULTS: As a result of comparing the classification model performance for sarcopenia prediction, the k-nearest neighborhood algorithm (kNN) classification model using 40 major features of TUG and 6mWT showed the best performance at 88%. CONCLUSION: This study can be used as a basic research for the development of self-monitoring technology for sarcopenia.

Mussel-inspired enzyme immobilization and dual real-time compensation algorithms for durable and accurate continuous glucose monitoring.

Blood glucose sensing is very important for diabetic management. It is shifting towards a continuous glucose monitoring because such a system can alleviate patient suffering and provide a large number of glucose measurements. Here, we proposed a novel approach for the development of durable and accurate enzymatic continuous glucose monitoring system (CGMS). For the long-term durable and selective immobilization of glucose oxidase on a microneedle electrode, a biocompatible engineered mussel adhesive protein was employed through efficient electrochemical oxidation strategy. For the accurate performance in in vivo environments, we also suggested dual real-time compensated algorithms to cover both temperature and time-lag differences. After pre-clinical and pilot-clinical evaluations, we confirmed that our proposed CGMS has an outstanding performance compared with various commercially available continuous systems and achieves comparable performance to disposable glucose sensors.

Comparison of enzymatic and non-enzymatic glucose sensors based on hierarchical Au-Ni alloy with conductive polymer.

Enzymatic and non-enzymatic amperometric glucose sensors based on nanostructured Au-Ni alloy were prepared and compared in their performance. The hierarchically structured Au-Ni surface was merely used for the non-enzymatic glucose sensor, while glucose oxidase attached poly-3'(benzoic acid) -2,2':5',2'- terthiophene (pTBA) formed on the alloy surface was used as the enzymatic sensor. The fabricated sensor was characterized using surface analysis and electrochemical experiments. In case of the enzymatic sensor, the anodic current of H2O2 generated from the enzyme reaction was used as the analytical signal, while the direct oxidation of glucose was observed on a mere Au-Ni alloy electrode without enzyme immobilization, which shows an excellent catalytic oxidation of glucose even in physiological pH. The potential pulse pretreatment of the sensor surfaces improved the performance, which allowed both the sensors reproducible and reusable (enzymatic sensor: coefficient of variation = 1.82%, n = 5, non-enzymatic: coefficient of variation = 2.93%). The enzymatic biosensor reveals the advantages of increased sensitivity, selectivity, and stability, compared with the non-enzymatic sensor. The linear range of enzymatic sensor was attained from 1.0 µM to 30.0 mM with a detection limit of 0.29 µM. The reliabilities of the sensors were also demonstrated through the glucose analysis in human blood samples, and the result was compared with the commercially available glucometer.

A selective glucose sensor based on direct oxidation on a bimetal catalyst with a molecular imprinted polymer.

A selective nonenzymatic glucose sensor was developed based on the direct oxidation of glucose on hierarchical CuCo bimetal-coated with a glucose-imprinted polymer (GIP). Glucose was introduced into the GIP composed of Nafion and polyurethane along with aminophenyl boronic acid (APBA), which was formed on the bimetal electrode formed on a screen-printed electrode. The extraction of glucose from the GIP allowed for the selective permeation of glucose into the bimetal electrode surface for oxidation. The GIP-coated bimetal sensor probe was characterized using electrochemical and surface analytical methods. The GIP layer coated on the NaOH pre-treated bimetal electrode exhibited a dynamic range between 1.0µM and 25.0mM with a detection limit of 0.65±0.10µM in phosphate buffer solution (pH 7.4). The anodic responses of uric acid, acetaminophen, dopamine, ascorbic acid, L-cysteine, and other saccharides (monosaccharides: galactose, mannose, fructose, and xylose; disaccharides: sucrose, lactose, and maltose) were not detected using the GIP-coated bimetal sensor. The reliability of the sensor was evaluated by the determination of glucose in artificial and whole blood samples.

Disposable all-solid-state pH and glucose sensors based on conductive polymer covered hierarchical AuZn oxide.

Poly(terthiophene benzoic acid) (pTBA) layered-AuZn alloy oxide (AuZnOx) deposited on the screen printed carbon electrode (pTBA/AuZnOx/SPCE) was prepared to create a disposable all-solid-state pH sensor at first. Further, FAD-glucose oxidase (GOx) was immobilized onto the pTBA/AuZnOx/SPCE to fabricate a glucose sensor. The characterizations of the sensor probe reveal that AuZnOx forms a homogeneous hierarchical structure, and that the polymerized pTBA layer on the alloy oxide surface captures GOx covalently. The benzoic acid group of pTBA coated on the probe layer synergetically improved the pH response of the alloy oxide and provide chemical binding sites to enzyme, which resulted in a Nernstian behavior (59.2 ± 0.5 mV/pH) in the pH range of 2-13. The experimental parameters affecting the glucose analysis were studied in terms of pH, temperature, humidity, and interferences. The sensor exhibited a fast response time <1s and a dynamic range between 30 and 500 mg/dL glucose with a detection limit of 17.23 ± 0.32 mg/dL. The reliabilities of the disposable pH and glucose sensors were examined for biological samples.

Interference Reduction in Glucose Detection by Redox Potential Tuning: New Glucose Meter Development.

A new glucose meter was developed employing a novel disposable glucose sensor strip comprising a nicotinamide adenine dinucleotide-glucose dehydrogenase (NAD-GDH) and a mixture of Fe compounds as a mediator. An iron complex, 5-(2,5-di(thiophen-2-yl)-1H-pyrrol-1-yl)-1,10-phenanthroline iron(III) chloride (Fe-PhenTPy), was synthesized as a new mediator for the NAD-GDH system. Due to the high oxidation potential of the mediator, the detection potential was tuned to be more closely fitted toward the enzyme reaction potential, less than 400 mV (vs. Ag/AgCl), by mixing with an additional iron mediator. The impedance spectrometry for the enzyme sensor containing the mixed mediators showed an enhanced charge transfer property. In addition, a new cartridge-type glucose meter was manufactured using effective aligned-electrodes, which showed an enhanced response compared with conventional electrode alignment. The proposed glucose sensor resulted in a wide dynamic range in the concentration range of 30 - 500 mg dL(-1) with a reduced interference effect and a good sensitivity of 0.57 µA mM(-1).

A label-free DC impedance-based microcytometer for circulating rare cancer cell counting.

Quantification of circulating tumor cells (CTCs) in blood samples is believed to provide valuable evidence of cancer progression, cancer activity status, response to therapy in patients with metastatic cancer, and possible cancer diagnosis. Recently, a number of researchers reported that CTCs tend to lose their epithelial cell adhesion molecule (EpCAM) by an epithelial-mesenchymal transition (EMT). As such, label-free CTC detection methods are attracting worldwide attention. Here, we describe a label-free DC impedance-based microcytometer for CTCs by exploiting the difference in size between CTCs and blood cells. This system detects changes in DC impedance between two polyelectrolytic gel electrodes (PGEs) under low DC voltages. Using spiked ovarian cancer cell lines (OVCAR-3) in blood as a model system, we were able to count the cells using a microcytometer with 88% efficiency with a flow rate of 13 µl min(-1) without a dilution process. Furthermore, we examined blood samples from breast cancer patients using the cytometer, and detected CTCs in 24 out of 24 patient samples. Thus, the proposed DC impedance-based microcytometer presents a facile and fast way of CTC evaluation regardless of their biomarkers.

Structural chemistry of M2Si5N8:Eu2+ (M = Ca, Sr, Ba) phosphor via structural refinement.

Structural refinement using X-ray powder diffraction data and geometry energy calculations using quantum mechanics were used to investigate the preferential substitution sites and the amount of Eu2+ ions in the host lattice of alkaline earth elements co-doped M2Si5N8:Eu2+ (M = Ca, Sr, and Ba), which is a red color-emitting nitride phosphor prepared via a carbothermal reaction method. Of the possible preferential sites, the preferential site proposed by the structural refinement results, in which the Eu2+ ions might preferentially occupy nine coordinated sites with nitrogen in M2Si5N8:Eu2+, was confirmed via geometry energy calculations using a first-principle based on the density-functional theory. The final converged weighted R factor (R(wp)) and the goodness-of-fit indicator [S(= R(wp)/R(e))] were 9.51% and 1.77, respectively. Each occupancy of Eu2+ ions for the two non-equivalent M sites, M(1) and M(2), was 0.10(2) and 0.04(2), respectively. The final refined model described the crystal structure in a space group Pmn2, (No. 31) with Z = 2, a = 5.7424(1) angstroms, b = 6.8837(1) angstroms, c = 9.3586(1) angstroms, and alpha(= beta= gamma)= 90 degrees.

Ion flow crossing over a polyelectrolyte diode on a microfluidic chip.

Key evidences are reported for the rectification mechanism of an aqueous ion diode based on polyelectrolytic plugs on a microfluidic chip by monitoring the ion flow crossing over the junction. The ion flow penetrating the polyelectrolyte junction is visualized by employing a fluorescent chemodosimeter, rhodamine B hydrazide and the pH-dependent dye, carboxy-fluorescein. How hysteresis phenomena, exhibited through the nonlinear behavior of the polyelectrolyte diode, are affected by a variety of parameters (e.g., switching potential, scan rate, and electrolyte concentration) is also investigated. The insights and knowledge from this study provide a crucial foundation for ion control at the iontronic diode in the aqueous phase, leading to more advanced aqueous organic computing devices and more diverse applications for microfluidic logic devices.

Ionic circuits based on polyelectrolyte diodes on a microchip.

Green means go: A polyelectrolyte diode on a microchip exhibits well-defined nonlinear rectifying behavior. This system visualizes the dynamic distribution of ions in a charged polymer phase under an electric field on a real-time basis using fluorescence images (see picture). Multiple polyelectrolyte diodes are integrated on a microchip to produce a variety of logic gates based on ionic circuits.

Red blood cell quantification microfluidic chip using polyelectrolytic gel electrodes.

This paper reports on a novel microfluidic chip with polyelectrolytic gel electrodes (PGEs) used to rapidly count the number of red blood cells (RBCs) in diluted whole blood. The proposed microdevice is based on the principle that the impedance across a microchannel between two PGEs varies sensitively as RBCs pass through it. The number and amplitude of impedance peaks provide the information about the number and size of RBCs, respectively. This system features a low-voltage dc detection method and non-contact condition between cells and metal electrodes. Major advantages include stable detection under varying cellular flow rate and position in the microchannel, little chance of cell damage due to high electric field gradient and no surface fouling of the metal electrodes. The performance of this PGEs-based system was evaluated in three steps. First, in order to observe the size-only dependence of the impedance signal, three different sizes of fluorescent microbeads (7.2, 10.0, and 15.0 mum; Bangs laboratories, USA) were used in the experiment. Second, the cell counting performance was evaluated by using 7.2 mum fluorescent microbeads, similar in size to RBCs, in various concentrations and comparing the results with an animal hematoanalyzer (MS 9-5; Melet schloesing laboratories, France). Finally, in human blood sample tests, intravenously collected whole blood was just diluted in a PBS without centrifuge or other pretreatments. The PGE-based system produced almost identical number of RBCs in over 800-fold diluted samples to the results from a commercialized human hematoanalyzer (HST-N402XE; Sysmex, Japan).