Performance evaluation of optical dissolved oxygen sensor, ARO-FT

The consumption of dissolved oxygen (DO) in water is indicative of aqueous organic content and therefore contamination in water1. Optical DO sensors consist of an oxygen sensitive fluorescence membrane on which oxygen can cause the quenching effect; the quenched fluorescence intensity is proportional to oxygen concentration2. These optical DO sensors are highly sensitive and long-term stable; however, the complex optical design and optical components make the cost always more expensive than electrochemical DO sensors. In order to reduce the cost, microfabricated optical DO sensing device is developed3; nevertheless, the sensitivity is sacrificed owing to the small sensing area resulting from miniaturization. Conventional optical DO sensing setup has single signal excitation site which contributes to the fact that the devices cannot provide sufficient signal intensity when being miniaturized (Fig. 1 (a)). In the light of this, we designed a multi-reflection (MR) optical DO sensor for overall sensitivity enhancement. Experimental results showed that the sensitivities can be increased by more than 3 times in MR sensors. In another aspect, biofouling is one of the major challenges of all water sensors4; therefore, we grafted polyethylene glycol (PEG) on the raw materials (polydimethylsiloxane, PDMS) of DO sensitive membrane. Reduction of protein adsorption (first step of biofouling) was observed as a result. Experiments Results and Discussions The optical scheme of MR optical DO sensor is shown in Fig. 1 (b). The fluorescence DO sensitive membrane was immobilized in a reservoir with total reflective (gold) surface at its bottom. A 455 nm laser was used as light source for generating fluorescence. A fluorescence-choosing band-pass filter is placed on top of the reservoir for not only preventing the excitation light from detected by a CCD sensor but also reflecting the excitation light into the reservoir again for MR purpose. After excitation, the generated fluorescence from membrane was collected by a convex lens and read by a commercially available spectrometer. The synthesis of DO sensitive membrane is guided by the following procedure: first, the PDMS elastomer (Dow Corning) was mixed with crosslinker at 10 to 1 weight ratio. Then 1 mg of the luminescent dye (Tris(bipyridine)ruthenium(II) chloride, Sigma Aldrich) was added to the polymer solution and stirred until uniformly mixed. The mixture was spin-coated on a three-inch silicon wafer at 4000 rpm for 30 second to obtain a membrane with 20 µm thickness. The DO sensing results suggest that the sensitivity is increased three times when using MR device as compared with the conventional setup.Contact angles of PDMS surfaces before and after PEG grafting are shown in Fig. 2 (a). The results show that the contact angle of PDMS is reduced significantly after PEG grafting (from 106.4 to 24.3), which illustrates the facts that the hydrophobicity of PDMS is reduced and that the protein (hydrophobic) absorption is restricted as showed in Fig. 2 (b). Conclusion The MR DO sensing device shows three times higher sensitivity as compared with signal excitation optical DO sensing setup. The result suggests that the multi-reflection device is a good replacement of miniaturized optical DO sensor. PEG grafting results in our experiments also show good anti-protein absorption capacity which may be effective in eliminating the biofouling progress. Reference 1. U.S. Environmental Protection Agency. in Volunteer Estuary Monitoring: A Methods Manual(U.S. Environmental Protection Agency) 9–3 (Office of Water, Washington, DC, 2006).2. McDonagh, C., Maccraith, B. D. & McEvoy, a K. Tailoring of sol-gel films for optical sensing of oxygen in gas and aqueous phase. Analytical chemistry 70,45–50 (1998).3. McEvoy, A., McDonagh, C. & MacCraith, B. Dissolved oxygen sensor based on fluorescence quenching of oxygen-sensitive ruthenium complexes immobilized in sol–gel-derived porous silica coatings. Analyst 121,785–788 (1996).4. Flemming, H.-C. Biofouling in water systems--cases, causes and countermeasures. Applied microbiology and biotechnology 59, 629–40 (2002).

Comparison of two Clark cell type dissolved oxygen sensors with three optical sensors in the Tualatin River, Oregon, indicated that the optical sensors were less prone to fouling drift and calibration drift. In two cleanings and calibrations over the 3-week study, the Clark cells exhibited fouling drifts ranging from 0.17 to 0.37 mg/L (milligrams per liter) and calibration drifts ranging from –0.22 to 0.03 mg/L. The optical sensors had fouling drifts ranging from 0 to 0.02 mg/L and calibration drifts ranging from –0.09 to 0.02 mg/L after 2–3 weeks of deployment. Measurements by the Clark cell and optical sensors compared well to each other and to point measurements of oxygen concentration using the Winkler method, indicating that the optical sensors were as accurate as the Clark cell sensors under the study conditions. Introduction The U.S. Geological Survey monitors dissolved oxygen (DO) concentration in the Tualatin River, west of Portland, Oregon, as part of a long-term assessment of the water quality of the river. (A description of the study can be found at http://or.water.usgs.gov/tualatin/) The Tualatin River study deploys polarographic, Clark cell type DO sensors as components of multiparameter datasondes that contain sensors for DO, temperature, pH, specific conductance, and turbidity. Clark cell sensors measure DO indirectly through an electrochemical reaction. The tip of the sensor contains a positive electrode (cathode) and a negative electrode (anode) connected electrically by a saturated electrolyte solution, all covered by a permeable Teflon membrane. Oxygen molecules dissolved in the water pass through the membrane and are chemically reduced within the sensor, generating an electrical current that is proportional to the oxygen concentration in the water. The current is converted to a DO concentration that is either displayed on a meter or stored as data for later retrieval. Clark cell DO sensors have been used for decades and provide accurate and precise DO data; however, they have drawbacks: (1) Clark cell units can require frequent calibration and maintenance. (2) Because oxygen is consumed at the surface of the membrane, water in that vicinity must be moving to obtain good measurements; in slow-moving water or in protective housings, mechanical stirring is necessary for most models, although YSI, Inc., has developed a technology that reportedly eliminates the need for stirring (http://www.act-us.info/Download/Do_Evaluations/ACT_VS04-04_YSI_DO.pdf, accessed March 3, 2006). (3) The Teflon membrane can be punctured by aquatic insects, improper handling, and waterborne debris. (4) Fouling of the membrane by algae and fine waterborne materials can significantly affect measurement quality; some units employ an automatic wiper to alleviate this problem. Optical DO sensors are a relatively new technology that can potentially reduce operating costs as a result of less-frequent required calibration and maintenance. Optical DO sensors have a tip coated on the inside with a thin layer of oxygen-sensitive fluorescent dye. A light-emitting diode (LED) shines blue light on the dye layer, causing the dye to emit red fluorescent light that travels to a photodetector. Oxygen diffusing into the sensor tip interferes with the light emitted by the dye, reducing the intensity of the light emitted, the amount of time the dye fluoresces, and the amount of time between blue light emission and

Immobilization of the oxygen-sensitive probes (OSPs) in the host matrix greatly impacts the performance and long-term usage of the optical dissolved oxygen (DO) sensors. In this work, fluorescent dyes, as the OSPs, were encapsulated with a crosslinked fluorinated polymer shell by interfacial confined reversible addition fragmentation chain transfer miniemulsion polymerization to fabricate oxygen sensitive polymeric nanocapsules (NCs). The location of fluorescent dyes and the fluorescent properties of the NCs were fully characterized by fourier transform infrared spectrometer, x-ray photoelectron spectrometer and fluorescent spectrum. Dye-encapsulated capacity can be precisely tuned from 0 to 1.3 wt% without self-quenching of the fluorescent dye. The crosslinked fluorinated polymer shell is not only extremely high gas permeability, but also prevents the fluorescent dyes from leakage in aqueous as well as in various organic solvents, such as ethanol, acetone and tetrahydrofuran (THF). An optical DO sensor based on the oxygen sensitive NCs was fabricated, showing high sensitivity, short response time, full reversibility, and long-term operational stability of online monitoring DO. The sensitivity of the optical DO sensor is 7.02 (the ratio of the response value in fully deoxygenated and saturated oxygenated water) in the range 0.96–14.16 mg l−1 and the response time is about 14.3 s. The sensor’s work curve was fit well using the modified Stern–Volmer equation by two-site model, and its response values are hardly affected by pH ranging from 2 to 12 and keep constant during continuous measurement for 3 months. It is believed that the oxygen sensitive polymeric NCs-based optical DO sensor could be particularly useful in long-term online DO monitoring in both aqueous and organic solvent systems.

The SBE 43 dissolved oxygen (DO) sensor is a complete redesign of the Clark electrode oxygen sensor and is engineered to provide stable, rapid-response dissolved oxygen measurements for profiling and long-term mooring applications. Customers as well as scientists at Sea-Bird are demonstrating that the SBE 43 DO sensor provides high quality moored DO data within 5 % accuracy for five or more months, even in high biological fouling coastal environments. As with all instruments, including optical DO sensors, biofouling ultimately interferes with the quality of moored measurements. When the SBE 43 DO sensor experiences a shift in calibration, it is primarily due to fouling of the membrane, which affects the slope of the sensor's response. The stable zero offset and the fact that the drift is confined to a linear slope means the calibration is easily corrected with a single reference point taken either in the field while the instrument remains moored, or during post processing of data after the sensor is recovered and validated in the lab.

Introduction Novel approaches including integration schemes (e.g. FinFET RMG) and new materials (e.g. Ge and III-V) for production are being studied. The introduction of Ge for CMOS device has shown interest in terms of advantage in the electron and hole mobility. However the use of Ge in CMOS integration is a new challenge in wet processing due to the significant Ge loss caused by oxidizers in liquid. Previous studies had focused on how to improve the process hardware with respect to Dissolved Oxygen (DO) concentration in liquid and oxygen concentration in ambient in wet processing. [1] This study focuses on the effect of Low DO condition for integration schemes, particularly two types of defect formation are used as representative metrics for the performance: the voids on Ge and the trench-formation in RMG on doped Si. [2] Experimental procedures (1) DO concentration measurement: The DO concentration in room temperature UPW and HF (0.5%) flowing though perfluoroalkoxy (PFA) tubing was measured using a DO concentration cell (HACH LANGE, 31120E.04). HF (0.5%)was prepared by co-mixing HF (49%) and UPW in line. Oxygen sensor (TORAY, LC-850KS) was used to measure oxygen concentration in ambient. (2) Selective Ni removal deposited on Ge : The sample shown as Fig. 1(a) was used to examine the generation of Ge voiding caused by galvanic corrosion in processing by various conditions of DO concentration in HCl (0.37%) and oxygen concentration in ambient. The generation of voiding was determined by SEM (AMAT, SEMVision G3) after wet processing. (3) Dummy oxide removal in high-k last process integration: The sample shown as Fig. 1(b) was used to examine the generation of Si channel trenching in processing by various conditions of DO concentration in HF (1.5%) and oxygen concentration in ambient. The generation of Si channel trenching was determined by TEM (FEI, Tecnai F30). Wet processing and DO concentration measurement were performed on a SCREEN Semiconductor Solutions single wafer cleaning tool (SU-3100). Results and Discussion Equipment improvements: Two points are key to reduce DO concentration in chemicals. The first key point is DO control in liquid. Table 1 shows the DO concentration in chemical at Point of Use (POU) with / without N2 purge to chemical tank or degassing module in line. This result shows that N2 purge and degassing module were effective to reduce the DO concentration in chemical. The second point is oxygen control in the wafer ambient environment during wet processing. Fig. 2 shows the oxygen concentration in ambient by using a shield-plate close to the wafer to block the atmosphere locally in combination with a N2 supply. By using the shield-plate, the oxygen concentration was controlled with less than 10 ppm, which resulted in only 0.44 ppb of dissolved oxygen based on Henry’s law. This concentration does not impact the DO concentration in chemical. By combining these two elements, the DO concentration in processing chemical can be reduced to 25ppb (HF 0.5%). Process results: Fig. 3 shows the NiGe loss on blanket wafer after processing in dHCl. A significant reduction of NiGe loss is obtained with Low DO process (25ppb). The prevention of void occurrence on Ge bulk FinFET device wafers is reported for the selective etch with the hot HCl process with low DO condition. Fig. 4 shows that the reduction of DO concentration in dHF can suppress Si channel trenching occurrence in condition of over etching and expand the process window. Conclusions It has been shown that the prevention of voiding occurrence on Ge and Si channel trenching occurrence was demonstrated by processing device samples with normal chemical with consideration to reduce the level of DO. The following two elements, “DO concentration in liquid” and “oxygen concentration in ambient in processing” are the key factors to achieve the low DO concentration processing.

Agricultural practices have the potential to influence hyporheic exchange through increased fine sediment loads and through reduced hydraulic conductivity, bed roughness and morphological diversity. These impacts can reduce connectivity between stream and hyporheic waters to the detriment of salmonid embryos. Salmonids bury their eggs in streambed gravels, typically to depths of up to 300 mm and for incubation periods of up to 6 months. Embryo survival is dependant on a complex range of factors which critically includes the delivery of oxygen from surface waters. This paper investigates hyporheic zone exchange processes, oxygen concentration and embryo survival in a canalised agricultural stream at a range of nested spatiotemporal scales. Results are contrasted with those from the Girnock Burn, a relatively undisturbed catchment. Conservative tracer experiments were used to assess reach average hyporheic exchange using the USGS OTIS model. Artificial redds were used to assess reach scale variability in hyporheic processes. Incubation stacks were used to assess embryo mortality and hyporheic water quality with depth at the scale of individual redds. Optodes (optical dissolved oxygen sensors) were used at a sub-set of sites to assess fine scale temporal variability in hyporheic oxygen and temperature. Stream and hyporheic hydrochemistry were used to infer source water contributions and provenance. Data showed that reach average hyporheic exchange in the Newmills Burn was ca. five times less than in the Gimock Burn. Dissolved oxygen (DO) concentrations related strongly to spatiotemporal patterns of groundwater (GW) discharge. Embryo survival was significantly correlated with DO. It is suggested that low DO in the Newmills Burn relates to groundwater upwelling and limited hyporheic exchange caused by a combination of low morphological diversity, hydraulic conductivity and bed roughness. It is suggested that future studies of embryo survival should look beyond the single issue of fine sediment effects to include a broader understanding of hyporheic zone processes.

Impact of Arterial Oxygen Tension on Venous Oxygen Saturation To the Editor We read with great interest the article “Influence of Arterial Dissolved Oxygen Level on Venous Oxygen Saturation: Don’t Forget the Pao2!” published ahead of print in Shock (1). First, we noted that the design of this study was exactly the same as an article we published in Shock in 2008 (2), in which inspired oxygen concentrations were increased to 100% transiently, and differences in central and mixed venous oxygen saturations in relation to changes in arterial oxygen tension were compared. We believe it will be beneficial to the readers of Shock to understand that a similar study had been performed and also similar findings were observed. Second, we agreed with the authors that partial oxygen tension of the central (Pvo2) (or mixed) venous blood has a significant bearing on the central venous (Scvo2) (or mixed venous oxygen) saturation. We believe it is a common misunderstanding that the difference between oxygen delivery and oxygen consumption is the main, if not the only, factor in determining Scvo2 (or mixed venous O2) saturation. Our previous work clearly demonstrated that a substantial increase in Scvo2 (and mixed venous oxygen saturation) due to an increase in arterial oxygen tension was more consistently observed than after a 10% change in cardiac index in critically ill patients with circulatory failure who required inotropic or vasopressor support (2). Furthermore, any increases in Scvo2 (or mixed venous oxygen) saturation due to an increase in arterial oxygen tension would confound its associations with the cardiac output status of the patients, rendering a “good” Scvo2 (or mixed venous oxygen) saturation uninterpretable as a marker of adequate cardiac output or oxygen delivery (3). Our observations and interpretations of the effect of arterial oxygen tension on Scvo2 (or mixed venous oxygen) saturation were also supported by a simulation study using mathematical modeling (4). Taking the results of the current study (1), our previous work (2,3), and the mathematical modeling study (4) together, we can conclude that arterial partial oxygen tension can have a substantial effect on Scvo2 (or mixed venous oxygen) saturation, making the suggestion that an adequate cardiac output or oxygen delivery is ensured when a “good” Scvo2 (or mixed venous oxygen) saturation is obtained invalid and misleading unless hyperoxemia is excluded. Any changes in Scvo2 can only be interpreted as reflecting changes in cardiac output and oxygen delivery if arterial oxygen tension is held constant. Finally, perhaps we all need to remember that it is the venous oxygen tension (Pvo2) that determines the venous oxygen saturation, and not the other way round. Increasing arterial oxygen tension will have a small but significant effect on venous oxygen tension (Pvo2), and the small change in venous oxygen tension (Pvo2) can have a substantial effect on Scvo2 (or mixed venous oxygen) saturation due to the steep part of the oxygen-hemoglobin dissociation curve when hemoglobin is saturated with oxygen between 50% and 90%. Kwok M. Ho, PhD, MPH Benjamin Silbert, MBBS Department of Intensive Care Medicine Royal Perth Hospital University of Western Australia Perth, Western Australia Australia

Dissolved oxygen (DO) is an important indicator for water quality and is also used in point of care applications. Fluorescence signal from Ruthenium (Ru(dpp)3 2+ ) based fluorophores can be quenched by oxygen such that the reduction of fluorescence signal is proportionally to oxygen concentration. This mechanism allows an optical method to measure DO in liquid. Although optical DO measurements offer high sensitivity and stability, they are also expensive, bulky, and difficult to use due to its complex design and requirement for specialized optical instruments such as light sources and spectrometers. Recently, the advances in microfabricated optical component including waveguides, lenses and mirrors, light sources, and photo detectors enable the integration of optical sensing and microfluidics sampling platform. We report the development of a total internal reflection assisted (TIRA) optical DO sensor for sensitivity enhancement. The excitation light is conducted down the water channel direction in the microfluidic device, while being confined within glass slide by total internal reflection. In addition to steady state intensity measurements, oxygen quenching is measured in the frequency domain using modulated light sources and synchronized detection systems. Experimental results show that optical sensitivity can be increased up to an order of magnitude in TIRA sensors. These results suggest the potential of TIRA scheme as a sensing and characterizing platform for optofluidic sensors.

OPTIMALIZATION OF OXYGEN LEVELS IN ROOT SYSTEMS AS EFFECTIVE CULTIVATION TOOL

Dissolved oxygen concentration is considered the most important water quality variable in fish culture. Reliable and continuous (24/7) oxygen monitoring of dissolved oxygen (DO) in the 1-11 mg/L range would be of great benefit to the aquaculture industry. We briefly review selected DO sensors from both the Clark and optical sensor categories as well a comparing their differences, both advantages and disadvantages. We introduce our fiber optic technique for continuous monitoring of DO levels in a flowing aqueous stream. An inorganic molybdenum chloride compound was used as the optical indicator in the oxygen sensitive material. The reflection mode fiber sensor is based on the ability of oxygen to quench the red luminescence of the molybdenum chloride indicator. The advantage of our broad-band, optical dissolved oxygen sensor is shown and discussed.

This work investigates a novel usage of aluminum-doped ceria nanoparticles (ADC-NPs), as the molecular probe in optical fluorescence quenching for sensing the dissolved oxygen (DO). Cerium oxide (ceria) nanoparticles can be considered one of the most unique nanomaterials that are being studied today due to the diffusion and reactivity of oxygen vacancies in ceria, which contributes to its high oxygen storage capability. Aluminum can be considered a promising dopant to increase the oxygen ionic conductivity in ceria nanoparticles which can improve the sensitivity of ceria nanoparticles to DO. The fluorescence intensity of ADC-NPs, synthesized via chemical precipitation, is found to have a strong inverse relationship with the DO concentration in aqueous solutions. Stern-Volmer constant of ADC-NPs at room temperature is determined to be 454.6 M(-1), which indicates that ADC-NPs have a promising sensitivity to dissolved oxygen, compared to many presently used fluorophores. In addition, Stern-Volmer constant is found to have a relatively small dependence on temperature between 25 °C to 50 °C, which shows excellent thermal stability of ADC-NPs sensitivity. Our work suggests that ADC-NPs, at 6 nm, are the smallest diameter DO molecular probes between the currently used optical DO sensors composed of different nanostructures. This investigation can improve the performance of fluorescence-quenching DO sensors for industrial and environmental applications.

Eutrophication, caused by excessive nutrient accumulation, leads to oxygen depletion and water quality degradation in aquatic ecosystems. Core indicators such as dissolved oxygen (DO), biological oxygen demand (BOD), and chemical oxygen demand (COD) are critical to assessing eutrophic conditions. Advances in Internet of Things (IoT) and artificial intelligence (AI) have enabled real-time water quality monitoring, but practical implementations remain limited, especially in low-resource settings. This systematic review analyzed 28 peer-reviewed studies (2015–2025) selected via PRISMA guidelines from Scopus, Google Scholar, and Web of Science. Sensor performance, AI integration, and deployment challenges were assessed. In parallel, a novel low-cost IoT-based circuit using ESP32 and open-source platforms (Blynk, Arduino IDE) was constructed and field-tested to demonstrate feasibility of real-time multi-parameter monitoring in the absence of DO-specific sensors. Optical DO sensors showed the highest accuracy (90–96%), with BOD and COD sensors achieving moderate performance (78% and 75–82%, respectively). Predictive forecasting for DO using AI achieved an R² = 0.85. Practical testing of the prototype showed reliable readings for pH, temperature, turbidity, and TDS, with effective real-time data visualization via mobile and cloud dashboards. Despite budgetary constraints, the circuit demonstrated adaptability and scalability for future DO integration. IoT-based monitoring systems are effective for managing eutrophication, with significant accuracy gains through AI-enhanced analytics. The prototype system developed in this study represents a novel, scalable solution for water quality monitoring in resource-constrained contexts. Its low-cost architecture, real-time capabilities, and cloud connectivity offer a practical pathway for broader adoption of smart environmental sensing technologies. Future work should incorporate nano-coated DO sensors, hybrid cloud-local architectures, and extended deployment trials to enhance reliability and impact.

In biological cells and tissues environment, real-time monitoring and controlling dissolved oxygen (DO) provides critical information for studying cellular metabolism process, health status and pathological features. This paper developed an optical DO sensor based on fluorescence quenching principle, prepared tris(4,7-diphenyl-1,10- phenanthroline)ruthenium(II) dichloride complex sol-gel sensing film, and studied its sensing performance. The principle of this sensor is that dissolved oxygen has quenching effect towards the fluorescence emitted by ruthenium complex. So the fluorescence intensity is reduced due to the existence of DO. The measurement limit of DO was 10- 100%, the response time was 20s, and the resolution was 0.02. Compared to traditional dissolved oxygen electrode probe, this luminescent fiber had many advantages, such as smaller size, shorter response time and higher stability.

COMPARING THREE OXYGEN DELIVERY SYSTEMS

Getting the Most Out of Nocturnal Pulse Oximetry