The Bandaiko hot spring, located in Kusatsu Town, Gunma Prefecture, is characterized by its hyper-acidic nature with a pH level of 1.7 and remarkable flow rate of approximately nine tons per minute. Gunma Prefecture is exploring the possibility of modifying its existing heat exchange system to establish a binary power generation facility utilizing this hyper-acidic hot spring, marking a potential first in the world. However, in the existing heat exchange facility, scale accumulation of the current facility necessitates water washing roughly once a month, but the type of scale and the rate of accumulation rate are still unknown. To address this, hot spring water was sampled and chemically analyzed, and field tests simulating scale adhesion were conducted using this water. For evaluation, quartz glass coupons and a batch-type scale sensor were utilized. The accumulated scale was identified as elemental sulfur. The use of quartz glass coupons did not enable an assessment of the scale deposition rate based on weight changes. By contrast, an 18-d immersion test with batch-type scale sensor indicated a gradual decrease in transmittance over time. The decrease in this sensor's transmittance serves as a proxy indicator for material accumulation under static immersion conditions. As it is not possible to analyze the scale adhering to the titanium heat exchanger during operation, it does not directly indicate the rate of scale deposition. Analysis of deposits on the sensor surface and scale recovered during the water washing of the heat exchanger revealed that the scale was elemental sulfur. Further analysis revealed that the elemental sulfur, derived from the chemical composition of the hot spring water, was undersaturated within the tested temperature range. The hot spring water is transported via pipeline to the heat exchange facility after gas-liquid separation at the source—located 2 km away—yet it is determined that atmospheric air enters the water at the source. This suggests that the precipitation of sulfur is caused either by the oxidation of trace amounts of H2S in the hot spring water by atmospheric oxygen or, alternatively, by bacterial activity. A subsequent bacterial analysis detected sulfur-oxidizing bacteria. These findings suggest that the formation of elemental sulfur scale likely results from the precipitation of sulfur caused by H2S oxidation—driven either by microbial activity or atmospheric oxygen—during the transport of the hot spring water. While installing sterilization equipment is an option for inhibiting bacterial activity, it entails significant costs. Given that the periodic water cleaning currently employed effectively restores heat exchange efficiency, this method remains the most appropriate approach for the time being. However, if the concentration of H2S in the hot spring water increases, reconsideration of a sterilization approach will be necessary. The novelty of this study is to connect observed sulfur scale, water chemistry, field sensor testing, equilibrium modelling, and microbial evidence in an actual utilization setting.

We established a reagent-free one-step electrochemical binding assay for cholera toxin (CT) using magnetic microbeads functionalized with pyrroloquinoline quinone (PQQ) as an electroactive compound and lactose as the ligand for CT. The detection principle in this assay is based on "sequestration electrochemistry", i.e., the binding of CT to the lactose portion immobilized on the magnetic microbead surface causes a decrease in the electrochemical response of PQQ, which is also immobilized by binding with lactose on the microbead surface. The voltammetric response of the PQQ-modified magnetic microbeads was measured using a magnetic carbon paste rotating-disk electrode, onto which the functionalized magnetic microbeads were adsorbed by rotating the electrode at 1000 rpm for 60 s. The response of the functionalized microbeads decreased with increasing the CT concentration. The specificity of the assay was confirmed by adding bovine g-globulin, which has a similar isoelectric point as CT, to the solution containing the functionalized microbeads. No decrease in the electrochemical response was observed in this case. After magnetic preconcentration, the limit of detection for CT was 58.8 ng ml-1. This simple and sensitive approach provides a rapid platform for CT detection and highlights the potential of sequestration electrochemistry for toxin monitoring in complex samples.

Wastewater from the batik textile industry contains diverse pollutants, including dyes, heavy metals, inorganic salts, and organic compounds, which are challenging to treat. Electroflotation has attracted increasing interest as a potential solution owing to its environmental friendliness and effectiveness against a wide range of pollutants. However, most previous studies have focused on improving electroflotation performance through anodic processes, while optimization of cathodic materials has received limited attention. In this study, nickel foam (NF) was investigated as a cathode material for the electroflotation treatment of batik wastewater. The NF cathode outperformed commercial electrodes due to its high electrical conductivity, large surface area, and low hydrogen evolution overpotential. Surface modification of NF via electrodeposition of nickel (NF/Ni) and nickel hydroxide (NF/Ni-OH) further enhanced electroflotation performance. Using an NF/Ni-OH cathode and a carbon rod anode in a NaCl electrolyte, the electroflotation process effectively removed dyes (Methyl Orange, 98.82%; Reactive Black 5, 99.87%; Methylene Blue, 97.75%), heavy metals (Cd, 58.7%; Cu, 45.3%; Zn, 91.4%; Cr(VI), 9.3%), and silicate (21.0%) at - 0.8 V vs Ag/AgCl over 60 min. The removal mechanisms of dyes, heavy metals, and silicates were elucidated, and the large surface area of NF-based cathodes was shown to enhance hydrogen bubble generation and floc flotation, thereby improving pollutant separation. These findings indicate that NF-based cathodic electroflotation is suitable for the simultaneous removal of dyes, silicates, and heavy metals such as Cd, Cu, and Zn from batik wastewater under optimized conditions, with good reproducibility and reusability over repeated cycles.

Paraquat (PQ), a highly toxic herbicide banned in several countries yet still widely used globally, poses severe threats to human health and ecosystems through acute poisoning and chronic exposure via contaminated food and water. Despite numerous analytical methods, rapid, sensitive, and field-deployable detection remains essential for effective monitoring and regulatory enforcement. Unlike existing reviews focusing narrowly on specific nanomaterials or detection techniques, this review represents a systematic cross-platform comparison evaluating metallic nanoparticles (Au, Ag, Pt), carbon-based materials (graphene, carbon nanotubes, quantum dots), metal-organic frameworks, and hybrid nanocomposites across electrochemical detection mechanisms. Critically, this review examines how food and environmental matrix effects influence sensor performance and discusses the analytical validation requirements necessary for reliable paraquat determination, thereby addressing a major gap in studies that predominantly report performance under idealized buffer conditions. Novel enhancement strategies are evaluated, including molecularly imprinted polymers, aptamer functionalization, and disposable electrode integration for point-of-use testing. This review uniquely addresses the translational research gap by identifying why promising laboratory sensors fail in real-world applications, including challenges associated with matrix interference, selectivity, long-term stability, reproducibility, and practical validation based on reports over the past decade. Furthermore, economic feasibility and lifecycle aspects of nanomaterial-enabled sensing platforms are critically discussed to evaluate their potential for deployment in resource-limited settings. Thus, the review provides clear guidance for developing next-generation sensors capable of protecting public health through effective paraquat monitoring.

Abstract Indonesian batik is a wax-resist dyeing technique of significant cultural and economic value; however, it also generates substantial environmental pollution, primarily in the form of wastewater contaminated with various heavy metals and dyes. This study investigated rice husks as a low-cost, effective, and sustainable adsorbent for treating batik effluent. Three potential adsorbents were tested, namely, rice husks, NaOH-treated rice husks, and FeCl3-treated rice husks. The results showed that further additives, such as pH control, FeCl2, and PAC (polyaluminum chloride), were added to improve the removal efficiency of heavy metals and dyes. The application of rice husk adsorbents with additive enhancement (i.e., FeCl2 (RHF2)) demonstrated high removal efficiencies of 97, 100, and 97% for methyl orange, reactive black, and methylene blue, respectively. Furthermore, the removal rates of heavy metals were 99, 99, 88, and 98% for Cd, Cr, Cu, and Zn, respectively. This method can also reduce the strong alkaline pH of batik effluent from 10.0 to 6.5. The high removal efficiency observed can be attributed to interactions between hydroxyl groups on the rice husks and Fe2+ ions from FeCl2, which facilitated the formation of Fe(OH)2 complexes, which promoted the aggregation of dyes and heavy metals via coprecipitation and generated additional active adsorption sites. Microtox analysis demonstrated that RHF2 effectively reduced the toxicity of the batik effluent for enhanced environmental safety. These results support the use of rice husks as a scalable and sustainable solution for treating batik effluent.

A simple yet highly sensitive analytical platform is presented that integrates solid-phase extraction using sedimentable dispersed particulates (SPE-SDP) with image-based fluorometric and colorimetric detection. In this strategy, dispersed particulates function simultaneously as extraction media and sedimentable optical sensing sites, enabling efficient analyte enrichment and direct signal readout without filtration or complex pretreatment. Resorufin, employed as a model fluorescent analyte, is rapidly captured onto silica gel via ion-pair formation with a cationic counterion (Zephiramine, Zeph+), allowing direct visual and quantitative evaluation of the settled phase. Systematic investigation of the adsorption behavior revealed that the capture process is governed by Langmuir-type adsorption of Zeph+ onto the silica surface. These findings indicate that Zeph+ acts not only as a counterion but also as an adsorption mediator, thereby promoting selective accumulation of resorufin on the solid phase and efficient localization of optical signals. Quantification was achieved through digital image analysis of the deposited particulates under visible or UV illumination, providing reliable optical information comparable to conventional spectrometric measurements. Under visible light, linear calibration was obtained over the concentration range of 0.1–2.0 μM with a detection limit of 80 nM (3σB), whereas fluorescence imaging provided a lower detection range of 0.01–0.2 μM with a detection limit of 7 nM. The analytical utility of the platform was further demonstrated by enzymatic determination of hydrogen peroxide using the Amplex Red–peroxidase system, achieving a detection limit of 0.28 μM (3σB). Successful application to river water and rainwater samples confirms the practicality of this approach for sensitive on-site environmental analysis. Owing to its reliance on measurable fluorescence and colorimetric responses, the proposed method represents a versatile optical sensing platform applicable to a broad range of optically detectable molecular and biomolecular targets.

The role of nanostructured materials in effective sensing, identification, and removal of NMPs from the environment is reviewed, emphasizing their unique structural and functional properties.

ABSTRACT Scale formation caused by the precipitation of inorganic minerals is a major operational challenge in geothermal systems, compromising heat transfer and causing equipment fouling. This study is the first to report a surface plasmon resonance (SPR) sensor based on a hetero‐core fiber‐optic architecture for the real‐time monitoring of geothermal scale formation. Its fiber‐optic configuration enables highly reproducible sensor fabrication without manual cladding removal, ensuring consistent sensor performance. The reproducibility and refractive‐index sensitivity of the proposed sensor are evaluated and compared with those of a conventional unclad‐fiber sensor. The sensor exhibits significantly reduced signal variability and enhanced sensitivity. When tested through the laboratory‐scale deposition of representative geothermal scale species, it produces clear, reproducible SPR peak shifts. Field tests at three geothermal sites demonstrate its practical advantages. Notably, silica‐dominant scale species, which cannot be quantitatively evaluated using conventional fiber sensors, are successfully detected through SPR peak shifts under field conditions. In addition, scale deposition rates, which are evaluated within approximately 15 h using conventional gravimetric methods (∼8.7 mg cm−2 h−1), are assessed within only a few hours using the SPR sensor. Thus, the hetero‐core fiber‐optic SPR sensor is an effective platform for the rapid in situ monitoring of geothermal scale formation.

The article deals with 2D nanomaterials and their special characteristics in view of their applications in detection and elimination of waterborne pathogens.

Monitoring dissolved CO2 under high-pressure conditions is important for subsurface environments relevant to geological sequestration. In this study, we report mid-infrared CO2 absorbance measurements using compact attenuated total reflection (ATR) fiber-optic sensors. Two fluoride-fiber probes-a side-polished ZBLAN fiber and a tapered InF3 fiber-were fabricated and evaluated in a pressure-and temperature-controlled system at 40 degrees C up to 8 MPa. CO2 was detected in gaseous, aqueous, and supercritical states via distinct absorption features near 4.2 mu m. In the aqueous phase, the ZBLAN sensor showed an approximately linear response and achieved a limit of detection of 7.03 mmol/L, while the InF3 sensor enabled reliable detection of gaseous and supercritical CO2. These results demonstrate phase-resolved CO2 sensing with fluoride-fiber ATR probes under sequestration-relevant conditions and support their potential for in situ monitoring in subsurface systems, including geological sequestration and carbon-recycled geothermal applications.

Batik is a traditional Indonesian textile that was declared a UNESCO Intangible Cultural Heritage in 2009. The batik industry, which originated from micro, small, and medium enterprises (MSMEs), has successfully driven the micro- and microeconomy. Batik production involves several stages that require the use of various chemicals, resulting in the generation of hazardous effluent. This effluent contains harmful contaminants, such as dyes, heavy metals, and organic/inorganic compounds, which pose environmental and health risks. Due to limitations in facilities, batik effluent is often improperly treated. Effective and efficient wastewater treatment solutions are needed, especially for MSMEs, which dominate the batik industry in Indonesia. This manuscript describes the potential contaminants arising from batik production, implemented countermeasures and treatment methods, and recommended low-cost, effective treatment methods considering the conditions of MSMEs. Several findings on contaminants from batik production should be addressed immediately by government regulation and by MSMEs through appropriate treatment methods. Appropriate treatment of batik waste not only protects and conserves the health of the surrounding environment but also improves the sustainability of the microeconomy of the community and the preservation of batik culture itself.

This study introduces a method for enhancing spectroelectrochemical sensor sensitivity by incorporating optical fiber technology. The sensor comprises a gold mesh electrode coated on the surface of an exposed optical fiber core. Total reflection attenuation spectroscopy was employed to measure the optical properties of the fiber core surface. To enhance sensitivity, we investigated surfactant addition to the sample, anticipating the formation of an electrostatic film on the optical fiber core surface. Spectroscopic measurements were conducted on 24 dyes, including cationic methylene blue and anionic indigosulfonic acid, as target substances. Consequently, adding surfactant at approximately one-tenth of the critical micelle concentration slightly improved the measurement sensitivity for cationic dyes, with a 2.3-fold increase observed for methylene blue. Previously challenging anionic dyes were successfully detected using this method. In addition, this technique was successfully applied to sulfide ion determination using the absorbance spectrophotometric method with methylene blue. The findings indicated that this approach markedly enhances the sensitivity and adaptability of spectroelectrochemical sensors using fiber optic, particularly in the detection of a wide variety of chemical substances.

A simple analytical method for screening Mn concentrations is useful for environmental water management. Herein, a simple analytical method for Mn2+ based on visual and image colorimetric analysis was developed by considering the adsorption of MnO4-, a colored substance, on sedimentable dispersed fine particles. The analyte could be determined by the visual or image analysis of the colored precipitates in a sample vessel. The extraction of MnO4-was achieved using fine silica gel particles modified with trimethylaminopropyl groups as an adsorbent. The established method can determine Mn2+ concentrations within approximately 1 min by simply adding the water sample to a tube containing the reagents and adsorbent particulates. The calibration curve shows good linearity in the range of 0.1 to 1.0 ppm. The limit of detection of image colorimetry using a light box and camera was 0.05 mg/L (3 sigma). The method was used to analyze Mn2+ in groundwater, and the results were cross-checked with the values obtained by atomic absorption spectrometry. Finally, the proposed method was successfully applied to the simple measurement of chemical oxygen demand using MnO4-as an oxidizing agent. The analyttical time for COD is just over 3 min.

This study successfully monitored the formation of secondary minerals resulting from CO2–H2O–rock reactions under high-temperature, high-pressure conditions (approximately 250 °C and 6 MPa, respectively) in real time using a sensor based on the attenuated total reflection (ATR) detection principle. First, a verification experiment was conducted using a saturated calcium carbonate solution. This experiment quantitatively confirmed an increase in precipitation and a decrease in transmittance as the temperature increased from 25 °C to 250 °C. Next, CO2–H2O–rock reaction tests were conducted within a batch-type apparatus. Under neutral conditions (pH 7.3), the transmittance rapidly decreased to approximately 20% within five days of initiating the reaction. Combined with our previous results from separate batch-based rock reaction tests conducted under identical conditions, it was revealed that the rapid precipitation of secondary minerals, primarily smectite, was the dominant process. Conventional methods estimate precipitation amounts by analyzing rock surface morphology after reaction tests, which leaves the reaction mechanism unclear. The primary innovation of this study lies in directly capturing precipitation dynamics during the initial reaction stage, which could not be achieved using conventional post reaction analysis methods. By employing this monitoring technique to measure the precipitation rates and quantities of secondary minerals under various test conditions, this study is expected to make significant contributions to the understanding and controlling of precipitation phenomena and changes in formation permeability in CO2 geological storage and carbon-recycling geothermal power generation projects.

Organic management is widely regarded as an effective strategy to prevent soil degradation in agroecosystems. In this study, we investigated the abundance of soil microarthropods in a multi-cropping system by comparing organic and conventional management practices. A total of 189 soil samples were collected from 63 agricultural sites cultivating three crops: paddy rice (Oryza sativa L.), soybeans [Glycine max (L.) Merrill], and vegetables [Cucurbita moschata (Duch.) Poir., Solanum melongena L., etc.]. An averaged generalized linear mixed model revealed that both organic management and vegetable cropping were associated with significantly higher microarthropod abundance. We also detected a positive interaction between the soil carbon-to-nitrogen ratio and organic nitrogen content, indicating that organically enriched soils provide favorable conditions for microarthropods. Our findings demonstrate that agricultural management practices, cropping systems, and soil nutrient profiles collectively shape the abundance of soil microarthropods.

Peat fires are recognized as a serious environmental problem in Indonesia and have a significant impact on both regional and global scales. Polycyclic aromatic hydrocarbons (PAHs) are environmental pollutants that are formed by the incomplete combustion of organic matter. The concentration and persistence of PAHs in post-fire soils are critical factors that must be thoroughly assessed. However, analyzing PAHs in peat soils is challenging, due to high organic content that can interfere with detection. The aim of this study was to develop a suitable GC/MS-based method for determining PAH in tropical peats and to evaluate PAHs at peat fire sites. The optimization of the method using PAH-spiked samples demonstrated that dichloromethane (DCM) was the optimal extraction solvent. Furthermore, the alkaline extraction significantly increased the recovery of PAHs. The post-fire PAH concentrations increased after peat fires, which were strongly associated with PAHs with three to four aromatic rings. The observation of temporal changes in PAHs at the same site indicated that PAHs produced by peat fires were retained in the burned sites for extended periods. Notably, a strong linear relationship was observed between Δa* soil color values and concentrations of 3–4 ring PAHs, suggesting that soil color can serve as a practical indicator of PAH contamination. This study has the potential to contribute to a better understanding of the behavior and risks of PAHs in post-fire peatlands in the future.

An electron-transfer/His-tag peptides-single-strand (ss) DNA probe is designed for the detection of cancer cells. Human myeloid leukemia cells (K562 cells) are commonly used as a model for target cancer cells. An electron-transfer peptide plays the role of a sensing moiety, and a His-tag moiety is introduced to purify the probe. A KK1B10 aptamer conjugated with the peptide sequence as an ss-DNA with target cell recognition properties is used. A probe with cysteine residue at the N-terminals is then immobilized on an Au screen-printed electrode (AuSPE). To evaluate the effect of the amino acid sequence in the probe, three types of probes are synthesized. The acetylated(Ac)-CYYCYYCH6-amino modifier C6(AmC6)KK1B10 aptamer probe proves to be a superior version. The K562 cells can interact with the probe on the electrode, and the electrode responses of the probe are decreased with increases in the concentrations of the cells. The peak currents are proportional to the concentrations of the cells and ranges from 5 to 200 cells mL with a detection limit of 2 cells/mL. The recovery 99%-102% of K562 cells in human serum and bovine blood is calculated using the probe-modified AuSPE. Consequently, the proposed method can be applied to the detection of target cells.

A novel technology called “Carbon Recycling $\text{CO}_{2}$ Geothermal Power Generation” aims to expand the deployment of geothermal power by enabling electricity generation even in non-hydrothermal regions. In this system, there is a possibility that a portion of the injected $\text{CO}_{2}$ is expected to undergo mineralization and be immobilized as scale deposits, primarily carbonate minerals. Monitoring scale formation is essential for effective facility maintenance. We have developed optical fiber sensors capable of quantitatively determining scale generated in geothermal fluids in real time within a brief period, and it is called “scale sensor”. However, the scale sensors that have been reported are fabricated by manually removing the cladding, thus this process makes it difficult to maintain high reproducibility when downsizing them. To address this issue, we developed a novel sensor based on a hetero-core optical fiber utilizing surface plasmon resonance (SPR). The sensor proposed in this study allows for easy and consistent fabrication. The performance of sensor was demonstrated to monitor the formation of silica scale in both laboratory and field tests.

Charge-transfer-type fluorochromes, which exhibit shifts in fluorescence intensity and emission wavelength in response to solvent polarity changes, have been widely employed to investigate solute-solvent interactions. Humic substances (HSs) are naturally occurring macromolecular organic acids derived from plant residues, with structural properties that vary depending on their origin and environmental conditions. The polarity of HSs is closely associated with the mobility and toxicity of environmental pollutants, making their chemical characterization essential. In this study, we developed a rapid and straightforward method to characterize HS polarity using fluorescent solvatochromism. The fluorescence peak shifts of four dyes-8-anilino-1-naphthalenesulfonic acid (ANS), acridine orange (AO), methylene blue (MB), and Rhodamine B (RhB)-were evaluated in the presence of humic acids (HAs), a major component of HSs. To assess environmental variability, a total of twelve HS samples were tested, including HSs derived from soils of different origins, compost, commercial reagents, and standard reference materials. Among these, AO and MB exhibited distinct spectral shifts without overlapping with the intrinsic fluorescence of HAs. Notably, MB displayed a consistent blue shift dependent on HA concentration, with the most stable response observed at 5 mg/L. The magnitude of this shift was significantly correlated with UV-Vis parameters associated with the aromaticity, humification degree, and polarity of HSs. Overall, this study demonstrates that MB-based fluorescent solvatochromism can function as an empirical and facile indicator for assessing the structural and microenvironmental characteristics of HSs, providing a rapid and complementary screening approach for HSs extracted and purified from environmental samples.