Monitoring of fluoride in water samples using a smartphone

Low cost materials for fluoride removal from groundwater

In several parts of the world, high fluoride concentrations in groundwater have been reported.Fluoride concentrations above the World Health Organization's (WHO) threshold level of 1.5 mg/L in drinkable water pose a health concern for communities and the environment. The distribution of fluoride is mainly related to the geological environment: rocks that contain fluorine, for example basalt, shale, and granite, release their respective minerals containing fluoride to the groundwater by dissolution. Excessive fluoride intake leads to dental and skeletal fluorosis, fragile bones, cancer, infertility, damage to the brain function, Alzheimer syndrome, and thyroid disorder. Cheap, abundant, and locally available fluoride removal techniques are needed to meet the requirement for fluoride-free drinking water in developing countries, especially in rural communities. Different conventional methods, such as membrane technologies, ion exchange, coagulation and precipitation techniques, are employed to remove fluoride from drinking water. However, only a few of these techniques can be applied at large-scale in developing countries due to their high investment costs, high maintenance and operating costs, and the possibility of producing toxic intermediates during the treatment process. Unlike conventional methods, adsorption is a promising technology due to its simple operation in a batch or continuous systems, simple design, low-cost of operation and wide range of locally available adsorbents. Adsorption is widely applied for removing fluoride from groundwater and wastewater, effectively maintaining water quality and taste. Based on the review, adsorption stands out as the best method for fluoride removal, considering surface modification and regeneration to increase the efficiency of adsorbent materials. This makes it an ideal solution for ensuring safe drinking water in resource-limited settings.

Conventional and advanced detection approaches of fluoride in water: a review

Fluorine is a naturally occurring element found in soil, water, food materials, and natural minerals such as fluorapatite, sellaite, and cryolite and exists as fluoride compounds with other elements because of high reactivity. The exposure of fluoride to the environment and human beings are industrial factors, food, water, and geogenic factors that impact the health of millions of human beings worldwide. Overexposure to fluoride exceeding the permissible limit (1.5 mg/l as per WHO) causes several diseases in human beings, such as teeth mottling, thyroid inflammation, dental fluorosis, skeletal fluorosis, lesions in the kidney, and other organs. To overcome the deleterious impact of fluoride, its detection at an early stage is very much required. Therefore, feeling the importance of the same, immense efforts have been made to the selective and sensitive determination of fluoride in water by numerous researchers. This review paper summarizes the various conventional methods such as spectroscopic, ion chromatography, ICP-OES, and gas chromatography-mass spectrometry, their advantages, and drawbacks leading to the development of advanced ready-to-use detection strategies such as stamartphones for on-the-spot fluoride detection. This review paper also discusses future directions, which will assist scientists in achieving a new benchmark in developing a reliable, cost-effective, and user-friendly fluoride detector.

Forward-Looking Roadmaps for Long-Term Continuous Water Quality Monitoring: Bottlenecks, Innovations, and Prospects in a Critical Review

Long-term continuous monitoring (LTCM) of water quality can bring far-reaching influences on water ecosystems by providing spatiotemporal data sets of diverse parameters and enabling operation of water and wastewater treatment processes in an energy-saving and cost-effective manner. However, current water monitoring technologies are deficient for long-term accuracy in data collection and processing capability. Inadequate LTCM data impedes water quality assessment and hinders the stakeholders and decision makers from foreseeing emerging problems and executing efficient control methodologies. To tackle this challenge, this review provides a forward-looking roadmap highlighting vital innovations toward LTCM, and elaborates on the impacts of LTCM through a three-hierarchy perspective: data, parameters, and systems. First, we demonstrate the critical needs and challenges of LTCM in natural resource water, drinking water, and wastewater systems, and differentiate LTCM from existing short-term and discrete monitoring techniques. We then elucidate three steps to achieve LTCM in water systems, consisting of data acquisition (water sensors), data processing (machine learning algorithms), and data application (with modeling and process control as two examples). Finally, we explore future opportunities of LTCM in four key domains, water, energy, sensing, and data, and underscore strategies to transfer scientific discoveries to general end-users.

Advances in Technological Research for Online and In Situ Water Quality Monitoring—A Review

Monitoring water quality is an essential tool for the control of pollutants and pathogens that can cause damage to the environment and human health. However, water quality analysis is usually performed in laboratory environments, often with the use of high-cost equipment and qualified professionals. With the progress of nanotechnology and the advance in engineering materials, several studies have shown, in recent years, the development of technologies aimed at monitoring water quality, with the ability to reduce the costs of analysis and accelerate the achievement of results for management and decision-making. In this work, a review was carried out on several low-cost developed technologies and applied in situ for water quality monitoring. Thus, new alternative technologies for the main physical (color, temperature, and turbidity), chemical (chlorine, fluorine, phosphorus, metals, nitrogen, dissolved oxygen, pH, and oxidation–reduction potential), and biological (total coliforms, Escherichia coli, algae, and cyanobacteria) water quality parameters were described. It was observed that there has been an increase in the number of publications related to the topic in recent years, mainly since 2012, with 641 studies being published in 2021. The main new technologies developed are based on optical or electrochemical sensors, however, due to the recent development of these technologies, more robust analyses and evaluations in real conditions are essential to guarantee the precision and repeatability of the methods, especially when it is desirable to compare the values with government regulatory standards.

Groundwater fluoride across the Punjab plains of Pakistan and India: Distribution and underlying mechanisms

Chronic exposure from drinking well-water with naturally high concentrations of fluoride (F^-) has serious health consequences in several regions across the world including South Asia, where the rural population is particularly dependent on untreated groundwater pumped from private wells. An extensive campaign to test 28,648 wells was conducted across the Punjab plains of Pakistan and India by relying primarily on field kits to document the scale of the problem and shed light on the underlying mechanisms. Groundwater samples were collected from a subset of 712 wells for laboratory analysis of F^- and other constituents. A handful of sites showing contrasting levels of F^- in groundwater were also drilled to determine if the composition of aquifer sediment differed between these sites. The laboratory data show that the field kits correctly classified 91% of the samples relative to the World Health Organization guideline for drinking water of 1.5 mg/L F^-. The kit data indicate that 9% of wells across a region extending from the Indus to the Sutlej rivers were elevated in F^- relative to this guideline. Field data indicate an association between the proportion of well-water samples with F^- > 1.5 mg/L and electric conductivity (EC) > 1.5 mS/cm across six floodplains and six intervening doabs. Low Ca²⁺ concentrations and elevated bicarbonate (HCO₃^- > 500 mg/L) and sodium (Na⁺ > 200 mg/L) in high F^- groundwater suggest regulation by fluorite. This could be through either the lack of precipitation or the dissolution of fluorite regulated by the loss of Ca²⁺ from groundwater due to precipitation of calcite and/or ion exchange with clay minerals. Widespread salinization of Punjab aquifers attributed to irrigation may have contributed to higher F^- levels in groundwater of the region. Historical conductivity data suggest salinization has yet to be reversed in spite of changes in water resources management.

A highly selective and sensitive CdS fluorescent quantum dot for the simultaneous detection of multiple pesticides

We presented one-pot prepared CdS fluorescent quantum dots (QDs) which can sensitively and selectively detect three different organic pesticides.

Health risk assessment of nitrate and fluoride in bottled water: a case study of Iran

Bottled water use has become widespread in recent years. Many Iranian cities are located in regions with a hot and semi-hot climate, and the quality of drinking water is low in most of these areas. Nitrate and fluoride are chemical constituents of drinking water with significant health concerns since they can be harmful in concentrations higher than drinking water standards. This study aims to determine nitrate and fluoride concentrations in different bottled water brands in the study region; evaluate the non-carcinogenic health risks posed by nitrate and fluoride exposure via the ingestion of bottled water; and compare the measured nitrate and fluoride concentrations with the amounts reported on the bottle labels. Twenty bottled water brands were sampled, and their nitrate and fluoride amounts were determined using the spectrophotometry method. The results revealed that 100% of nitrate and 70% of fluoride in samples had concentrations greater than the levels reported on bottle labels. Minimum, maximum, and mean concentrations for nitrate were, respectively, 1.1, 28, and 8.37 mg/L, and for fluoride were 0.014, 2.36, and 0.63 mg/L. The hazard quotient (HQ) values due to nitrate intake were > 1 in 10% of the samples (n = 2) for both infants and children, indicating potential adverse non-carcinogenic health effects upon consumption. For fluoride intake, the potential adverse health effects (HQ > 1) for infants, children, teenagers, and adults were respectively high in 30, 20, 10, and 10% of the samples. For nitrate, the 95th centile for infants was 1.547, and for fluoride, it was 2.62, 2.19, 1.15, and 1 for infants, children, teenagers, and adults, respectively.

Smartphone-enabled field monitoring tool for rapid hexavalent chromium detection in water

Chromium contamination of soil and water is a serious environmental and public health concern as the hexavalent form of chromium [Cr(VI)] is readily soluble in water and is a confirmed carcinogen. There is an imminent need for a robust, low-cost, and simple analytical technique to facilitate in situ monitoring of Cr(VI) in water. Current quantitative methods of Cr(VI) detection are largely laboratory-based, time-consuming, expensive, and require training for implementation. In this contribution, a portable, easy-to-use, and compact measuring tool is presented that provides Cr(VI) concentration within 10 min of water sampling over a linear range of 0-3 mg L^-1. This tool utilizes a relatively inexpensive camera-enabled smartphone with a custom-made test chamber attachment to seamlessly perform Cr(VI) measurements on water samples in the field. For analysis, an android-based software application was developed that directs the user to perform a simple series of steps following the diphenylcarbazide-based colorimetric method prescribed by the American Public Health Association. The tool was validated against a standard UV-visible spectrophotometer for a variety of synthetic and naturally contaminated water samples, with correlation factors greater than 0.993 (p < .001). The colorimetric method was also validated against a non-colorimetric Cr(VI) detection technique-ion chromatography-inductively coupled plasma mass spectrometry. Furthermore, Cr(VI) detection limits for the smartphone-enabled colorimetric method were found to be within 1.3-11.6 μg L^-1, which were significantly better than reported for commercially available field test kits, and even surpassed the limits exhibited by a typical spectrophotometer (25-50 μg L^-1). Finally, real-time mapping of source waters at a contaminated site was demonstrated by remote logging of Cr(VI) water quality data and corresponding GPS coordinates into a cloud server. This study highlights the potential role of smartphone-based monitoring tool in providing information to the affected community and enabling safe access to drinking water. An accurate, robust, simple-to-use, and economic method to measure hexavalent chromium in water within 10 min of sampling at site.

Recent trends in smartphone-based detection for biomedical applications: a review

Smartphone-based imaging devices (SIDs) have shown to be versatile and have a wide range of biomedical applications. With the increasing demand for high-quality medical services, technological interventions such as portable devices that can be used in remote and resource-less conditions and have an impact on quantity and quality of care. Additionally, smartphone-based devices have shown their application in the field of teleimaging, food technology, education, etc. Depending on the application and imaging capability required, the optical arrangement of the SID varies which enables them to be used in multiple setups like bright-field, fluorescence, dark-field, and multiple arrays with certain changes in their optics and illumination. This comprehensive review discusses the numerous applications and development of SIDs towards histopathological examination, detection of bacteria and viruses, food technology, and routine diagnosis. Smartphone-based devices are complemented with deep learning methods to further increase the efficiency of the devices. Graphical Abstract.

Textile-based wearable solid-contact flexible fluoride sensor: Toward biodetection of G-type nerve agents

Rising global concerns posed by chemical and biological threat agents highlight the critical need to develop reliable strategies for the real-time detection of such threats. While wearable sensing technology is well suited to fulfill this task, the use of on-body devices for rapid and selective field identification of chemical agents is relatively a new area. This work describes a flexible printed textile-based solid-contact potentiometric sensor for the selective detection of fluoride anions liberated by the biocatalytic hydrolysis of fluorine-containing G-type nerve agents (such as sarin or soman). The newly developed solid-contact textile fluoride sensor relies on a fluoride-selective bis(fluorodioctylstannyl)methane ionophore to provide attractive analytical performance with near-Nernstian sensitivity and effective discrimination against common anions, along with excellent reversibility and repeatability for dynamically changing fluoride concentrations. By using stress-enduring printed inks and serpentine structures along with stretchable textile substrates, the resulting textile-based fluoride sensor exhibits robust mechanical resiliency under severe mechanical strains. Such realization of an effective textile-based fluoride-selective electrode allowed biosensing of the nerve-agent simulant diisopropyl fluorophosphate (DFP), in connection to immobilized organophosphorus acid anhydrolylase (OPAA) or organophosphorus hydrolase (OPH) enzymes. A user-friendly portable electronic module transmits data from the new textile-based potentiometric biosensor wirelessly to a nearby smartphone for alerting the wearer instantaneously about potential chemical threats. While expanding the scope of wearable solid-contact anion sensors, such a textile-based potentiometric fluoride electrode transducer offers particular promise for effective discrimination of G-type neurotoxins from organophosphate (OP) pesticides, toward specific field detection of these agents in diverse defense settings.

Current progress in the utilization of smartphone-based imaging for quality assessment of food products: a review

The cell phone has been merely used for image acquisition and transmission in the last decades. Owing to the recent technological progress, its new generation, i.e., the smartphone, draws remarkable attention to food quality assessment with versatile applications. Smartphones possess high-resolution cameras, enabling them to be used instead of digital cameras in the computer vision system. Furthermore, their programmability and portability have recently encouraged researchers to introduce smartphone-based image processing in food analytical studies. This promising approach has advantages such as high sensing capability, being user friendly, and cost-effective over the conventional method, and therefore might be considered an emerging nondestructive technique for quality control purposes. However, there is a great effort to tackle implementation, calibration, as well as industrialization issues. In this context, this review aims to highlight the most recent studies of smartphone-based imaging systems in various food systems such as dairy, meat, fruit, and vegetables. Besides, the existing challenges and future trends for applying smartphones in food quality control are discussed. Although moving the computer vision systems toward a portable tool like a smartphone improves its versatility, more research works are needed to resolve its set-up weakness and limitations.

Smartphone-based Fluoride-specific Sensor for Rapid and Affordable Colorimetric Detection and Precise Quantification at Sub-ppm Levels for Field Applications

Higher levels of fluoride (F^-) in groundwater constitute a severe problem that affects more than 200 million people spread over 25 countries. It is essential not only to detect but also to accurately quantify aqueous F^- to ensure safety. The need of the hour is to develop smart water quality testing systems that would be effective in location-based real-time water quality data collection, devoid of professional expertise for handling. We report a cheap, handheld, portable mobile device for colorimetric detection and rapid estimation of F^- in water by the application of the synthesized core-shell nanoparticles (near-cubic ceria@zirconia nanocages) and a chemoresponsive dye (xylenol orange). The nanomaterial has been characterized thoroughly, and the mechanism of sensing has been studied in detail. The sensor system is highly selective toward F^- and shows unprecedented sensitivity in the range of 0.1-5 ppm of F^-, in field water samples, which is the transition regime, where remedial measures may be needed. It addresses multiple issues expressed by indicator-based metal complexes used to determine F^- previously. Consistency in the performance of the sensing material has been tested with synthetic F^- standards, water samples from F^- affected regions, and dental care products like toothpastes and mouthwash using a smartphone attachment and by the naked eye. The sensor performs better than what was reported by prior works on aqueous F^- sensing.

Estimation of PM10 Levels and Sources in Air Quality Networks by Digital Analysis of Smartphone Camera Images Taken from Samples Deposited on Filters

This paper explores the performance of smartphone cameras as low-cost and easily accessible tools to provide information about the levels and origin of particulate matter (PM) in ambient air. We tested the concept by digital analysis of the images of daily PM₁₀ (particles with diameters 10 µm and smaller) samples captured on glass fibre filters by high-volume aerosol samplers at urban and rural locations belonging to the air quality monitoring network of Extremadura (Spain) for one year. The images were taken by placing the filters inside a box designed to maintain controlled and reproducible light conditions. Digital image analysis was carried out by a mobile colour-sensing application using red, green, blue/hue, saturation, value/hue, saturation, luminance (RGB/HSV/HSL) parameters, that were processed through statistical procedures, directly or transformed to greyscale. The results of the study show that digital image analysis of the filters can roughly estimate the concentration of PM₁₀ within an air quality network, based on a significant linear correlation between the concentration of PM₁₀ measured by an official gravimetric method and the colour parameters of the filters’ images, with better results in the case of the saturation parameter (S_HSV). The methodology based on digital analysis can discriminate urban and rural sampling locations affected by different local particle-emitting sources and is also able to identify the presence of remote sources such as Saharan dust outbreaks in both urban and rural locations. The proposed methodology can be considered as a useful complement to the aerosol sampling equipment of air quality network field units for a quick estimation of PM₁₀ in the ambient air, through a simple, accessible and low-cost procedure, with further miniaturization potential.

Standardized spectral and radiometric calibration of consumer cameras

Consumer cameras, particularly onboard smartphones and UAVs, are now commonly used as scientific instruments. However, their data processing pipelines are not optimized for quantitative radiometry and their calibration is more complex than that of scientific cameras. The lack of a standardized calibration methodology limits the interoperability between devices and, in the ever-changing market, ultimately the lifespan of projects using them. We present a standardized methodology and database (SPECTACLE) for spectral and radiometric calibrations of consumer cameras, including linearity, bias variations, read-out noise, dark current, ISO speed and gain, flat-field, and RGB spectral response. This includes golden standard ground-truth methods and do-it-yourself methods suitable for non-experts. Applying this methodology to seven popular cameras, we found high linearity in RAW but not JPEG data, inter-pixel gain variations >400% correlated with large-scale bias and read-out noise patterns, non-trivial ISO speed normalization functions, flat-field correction factors varying by up to 2.79 over the field of view, and both similarities and differences in spectral response. Moreover, these results differed wildly between camera models, highlighting the importance of standardization and a centralized database.

Low Cost Wavelength Specific Water Quality Measurement Technique

Optical sensing for chemical analysis is emerging as it provides advantages such as good sensitivity, selectivity, electromagnetic immunity, etc. This work presents a low-cost, robust and easy to use technique for measurement of bulk water property changes, specifically pH, total dissolved solids (TDS), and turbidity. The designed multi-wavelength sensing mechanism is capable of measuring the absorption of light emitted by three different LEDs after passing through water. The optical responses obtained using this mechanism are then related to parameter changes of water for quality measurement. The results show that measurements for pH, TDS, and turbidity have a linear regression coefficient of 0.9691, 0.9729 and 0.76 respectively. By utilizing narrowband light sources of characteristic wavelengths for the target parameters, a compact and portable device can be designed for rapid measurements. This can work as a replacement of spectrophotometers for parameter specific measurements of water quality and a low cost prototype (costing ~ 20 $) for the same has been demonstrated.

Aptamer-Based Fluorescent Sensor Array for Multiplexed Detection of Cyanotoxins on a Smartphone

Developing easy-to-use and miniaturized detectors is essential for in-field monitoring of environmentally hazardous substances, such as the cyanotoxins. We demonstrated a differential fluorescent sensor array made of aptamers and single-stranded DNA (ssDNA) dyes for multiplexed detection and discrimination of four common cyanotoxins with an ordinary smartphone within 5 min of reaction. The assay reagents were preloaded and dried in a microfluidic chip with a long shelf life over 60 days. Upon the addition of analyte solutions, competitive binding of cyanotoxin to the specific aptamer-dye conjugate occurred. A zone-specific and concentration-dependent reduction in the green fluorescence was observed as a result of the aptamer conformation change. The aptasensors are fully optimized by quantification of their dissociation constants, tuning the stoichiometric ratios of reaction mixtures, and implementation of an internal intensity correction step. The fluorescent sensor array allowed for accurate identification and measurement of four important cyanotoxins, including anatoxin-a (ATX), cylindrospermopsin (CYN), nodularin (NOD), and microcystin-LR (MC-LR), in parallel, with the limit of detection (LOD) down to a few nanomolar (<3 nM), which is close to the World Health Organization's guideline for the maximum concentration allowed in drinking water. The smartphone-based sensor platform also showed remarkable chemical specificity against potential interfering agents in water. The performance of the system was tested and validated with real lake water samples that were contaminated with trace levels of individual cyanotoxins as well as binary, ternary, and quaternary mixtures. Finally, a smartphone app interface has been developed for rapid on-site data processing and result display.

Emerging Point-of-care Technologies for Food Safety Analysis

Food safety issues have recently attracted public concern. The deleterious effects of compromised food safety on health have rendered food safety analysis an approach of paramount importance. While conventional techniques such as high-performance liquid chromatography and mass spectrometry have traditionally been utilized for the detection of food contaminants, they are relatively expensive, time-consuming and labor intensive, impeding their use for point-of-care (POC) applications. In addition, accessibility of these tests is limited in developing countries where food-related illnesses are prevalent. There is, therefore, an urgent need to develop simple and robust diagnostic POC devices. POC devices, including paper- and chip-based devices, are typically rapid, cost-effective and user-friendly, offering a tremendous potential for rapid food safety analysis at POC settings. Herein, we discuss the most recent advances in the development of emerging POC devices for food safety analysis. We first provide an overview of common food safety issues and the existing techniques for detecting food contaminants such as foodborne pathogens, chemicals, allergens, and toxins. The importance of rapid food safety analysis along with the beneficial use of miniaturized POC devices are subsequently reviewed. Finally, the existing challenges and future perspectives of developing the miniaturized POC devices for food safety monitoring are briefly discussed.

A Hand-Held Point-of-Care Biosensor Device for Detection of Multiple Cancer and Cardiac Disease Biomarkers Using Interdigitated Capacitive Arrays

This paper presents a hand-held point-of-care device that incorporates a lab-on-a-chip module with interdigitated capacitive biosensors for label-free detection of multiple cancer and cardiovascular disease biomarkers. The developed prototype is comprised of a cartridge incorporating capacitive biodetection sensors, a sensitive capacitive readout electronics enclosed in a hand-held unit, and data analysis software calculating the concentration of biomarkers using previously stored reference database. The capacitive biodetection sensors are made of interdigitated circular electrodes, which are preactivated with single (for detecting one biomarker) or multiple specific antibodies (for detecting multiple disease biomarkers). Detection principle of capacitive biosensor is based on measuring the level of capacitance change between interdigitated electrode pairs induced by the change in dielectric constant due to affinity-based electron exchange in between antibodies/antigens and electrodes. The more antibody-antigens binding occurs, the more capacitance change is measured due to the change in dielectric constant of the capacitance media. The device uses preactivated ready-to-use cartridges embedded with capacitive biosensors with shelf-life of three months under optimal conditions, and is capable of onsite diagnosis and can report the result in less than 30 min. The device is verified with real patient blood samples for six different disease biomarkers.

Age-sex specific and sequela-specific disability-adjusted life years (DALYs) due to dental caries preventable through water fluoridation: An assessment at the national and subnational levels in Iran, 2016

We assessed disability-adjusted life years (DALYs) due to dental caries preventable through water fluoridation apportioned by sex, age group, sequela, province, and community type in Iran, 2016. The burden of disease due to dental caries was extracted from the Global Burden of Disease Study 2016 (GBD 2016) and the caries preventive effect of water fluoridation was calculated using a database of fluoride levels in drinking water. All the preventable DALYs were caused by years lived with disability (YLDs) because of the non-fatal character of dental caries. DALYs and DALY rate (per 100,000 people) preventable through water fluoridation at the national level in 2016 were 14,971 (95% uncertainty interval 7348- 24,725) and 18.73 (9.19-30.93), respectively. The national population preventable fraction (PPF) of dental caries by water fluoridation was determined to be as high as 0.176 (0.141-0.189). The share of sequelae in the preventable DALYs at the national level were estimated to be 76.8% for edentulism and severe tooth loss, 21.4% for caries of permanent teeth, and 1.8% for caries of deciduous teeth. The national DALYs and DALY rate preventable through water fluoridation exhibited no difference by sex, but considerably increased by age from 110 (37-223) and 1.5 (0.5-3.1) for the age group 0-4 y to 4331 (2334-6579) and 88.9 (47.9-135.1) for the age group 65 y and older, respectively. Over 80% of the national preventable DALYs occurred in urban areas due to higher population and lower coverage of fluoridated drinking water. The highest provincial DALYs and DALY rate preventable by water fluoridation were observed in Tehran and Gilan to be 3776 (1866-6206) and 37.2 (18.6-60.8), respectively. The results indicated that water fluoridation can play a profound role in the promotion of dental public health and compensate the spatial inequality and increasing temporal trend of health losses from dental caries at the national level.

"The Smartphone's Guide to the Galaxy": In Situ Analysis in Space

A human mission to Mars can be viewed as the apex of human technological achievement. However, to make this dream a reality several obstacles need to be overcome. One is devising practical ways to safeguard the crew health during the mission through the development of easy operable and compact sensors. Lately, several smartphone-based sensing devices (SBDs) with the purpose to enable the immediate sensitive detection of chemicals, proteins or pathogens in remote settings have emerged. In this critical review, the potential to piggyback these systems for in situ analysis in space has been investigated on application of a systematic keyword search whereby the most relevant articles were examined comprehensively and existing SBDs were divided into 4 relevant groups for the monitoring of crew health during space missions. Recently developed recognition elements (REs), which could offer the enhanced ability to tolerate those harsh conditions in space, have been reviewed with recommendations offered. In addition, the potential use of cell free synthetic biology to obtain long-term shelf-stable reagents was reviewed. Finally, a synopsis of the possibilities of combining novel SBD, RE and nanomaterials to create a compact sensor-platform ensuring adequate crew health monitoring has been provided.

Investigating the suitability of Fe0 packed-beds for water defluoridation

A commercial granular metallic iron (Fe⁰) specimen was used to evaluate the suitability of Fe⁰ materials for removing aqueous fluoride (F^-) (water defluoridation). Experiments were performed to characterize the defluoridation potential of the tested Fe⁰ as influenced by the presence of chloride (Cl^-) and bicarbonate (HCO₃^-) ions using tap water (H₂O) as operational reference system. Duplicate column studies were conducted for 120 days (4 months) using an initial F^- concentration of 22.5 mg L^-1, columns flow rates were about 17 mL h^-1. Each column contained a reactive layer (11 cm) made up of 100 g of Fe⁰ in a 1:1 volumetric Fe⁰:sand mixture. The reactive layer was sandwiched between two layers of the same sand. A pure sand column was used as control system. After the F^- removal experiments, the columns were flushed by methylene blue (MB) and Orange II for 21 days. Removal studies revealed (i) no F^- removal in the control system, (ii) no F^- significant removal on the Cl^- system, (iii) limited F^- removal in the HCO₃^- system, and (iv) the best F^- removal efficiency in tap water (H₂O). Dye flushing studies confirmed the ion-selective nature of the Fe⁰/H₂O system and demonstrated the relatively low efficiency of the same for F^- removal. The overall results challenge the prevailing perception that water defluoridation using granular Fe⁰ is not possible and suggest that effective water defluoridation in Fe⁰ packed-beds is pure a site-specific design issue.

Development and application of a low-cost smartphone-based turbidimeter using scattered light

We demonstrate the development and application of a low-cost smartphone turbidimeter system to be used on water samples collected from natural resources. The proposed system depends on the spectroscopic measurements of both forward- and side-scattered light. A custom-designed cradle was fabricated using 3D printing, and plastic optical fibers were used to couple light from the smartphone's built-in flash and transmit the collected scattered light to the camera sensor. The performance parameters of the smartphone turbidimeter were investigated and compared to commercial systems, and the lowest limit of detection was found to be 5.58 NTU for forward-scattered detection. The results obtained in the proposed scattered-light-based spectroscopic turbidimeter and the practicality achieved by this extremely low-cost device will have a great impact on water science and technology.

Azulene-boronate esters: colorimetric indicators for fluoride in drinking water

Low cost and in situ fluoride detection by non-experts is important for the determination of drinking water safety in developing countries. Colour reagents can provide results quickly without expensive equipment, but colorimetric fluoride indicators are often nonspecific, complex to use or do not work in water. Here we show that azulene-boronate indicators respond selectively to fluoride at concentrations relevant to the WHO limit of 1.5 mg L^-1.

Smartphone app-based/portable sensor for the detection of fluoro-surfactant PFOA

We developed a smartphone app-based monitoring tool for the detection of anionic surfactants (AS), including perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS). Akin to the methylene blue active substances (MBAS), liquid-phase extraction (LPE) is employed to extract the hydrophobic ion-pair of dye (ethyl violet)-AS to an organic phase (ethyl acetate). The colour (RGB) of the organic phase is read using a smartphone camera with the help of a reading kit. The value of RGB is carefully corrected and linked to the concentration of ASs with a standard deviation of <10% in the 10-1000 ppb (part per billion) range. In order to avoid the interference arising from inorganic anions (such as those found in tap water and groundwater), the water sample is pre-treated either by solid-phase extraction (SPE), which takes ∼30 min, or by dual liquid-phase extraction (dual-LPE, developed by us), which takes ∼5 min. In the latter case, the organic phase of the first LPE (equilibrium with water sample) is transferred and subjected to a second LPE (equilibrium with Milli-Q water) to remove any potential background interference. In the meantime, SPE can also pre-concentrate ASs at 100-1000 times (in volume) to benefit the sensitivity. Consequently, our smartphone app can detect PFOA spiked in tap/groundwater with an LOD of 10 ppb (∼12 nM, dual-LPE of ∼5 min), or 0.5 ppb (∼1.2 nM, SPE of ∼3 h), suggesting that it has the potential to succeed as a pre-screening tool for on-site application and in common laboratory tests.

Smartphone-Based Food Diagnostic Technologies: A Review

A new generation of mobile sensing approaches offers significant advantages over traditional platforms in terms of test speed, control, low cost, ease-of-operation, and data management, and requires minimal equipment and user involvement. The marriage of novel sensing technologies with cellphones enables the development of powerful lab-on-smartphone platforms for many important applications including medical diagnosis, environmental monitoring, and food safety analysis. This paper reviews the recent advancements and developments in the field of smartphone-based food diagnostic technologies, with an emphasis on custom modules to enhance smartphone sensing capabilities. These devices typically comprise multiple components such as detectors, sample processors, disposable chips, batteries and software, which are integrated with a commercial smartphone. One of the most important aspects of developing these systems is the integration of these components onto a compact and lightweight platform that requires minimal power. To date, researchers have demonstrated several promising approaches employing various sensing techniques and device configurations. We aim to provide a systematic classification according to the detection strategy, providing a critical discussion of strengths and weaknesses. We have also extended the analysis to the food scanning devices that are increasingly populating the Internet of Things (IoT) market, demonstrating how this field is indeed promising, as the research outputs are quickly capitalized on new start-up companies.

Microaxicave colour analysis system for fluoride concentration using a smartphone

Layout of our fluoride measurement system and the correlation between the concentration of fluoride and the peak of value–hue curves.

Low-Cost, Robust, and Field Portable Smartphone Platform Photometric Sensor for Fluoride Level Detection in Drinking Water

Groundwater is the major source of drinking water for people living in rural areas of India. Pollutants such as fluoride in groundwater may be present in much higher concentration than the permissible limit. Fluoride does not give any visible coloration to water, and hence, no effort is made to remove or reduce the concentration of this chemical present in drinking water. This may lead to a serious health hazard for those people taking groundwater as their primary source of drinking water. Sophisticated laboratory grade tools such as ion selective electrodes (ISE) and portable spectrophotometers are commercially available for in-field detection of fluoride level in drinking water. However, such tools are generally expensive and require expertise to handle. In this paper, we demonstrate the working of a low cost, robust, and field portable smartphone platform fluoride sensor that can detect and analyze fluoride concentration level in drinking water. For development of the proposed sensor, we utilize the ambient light sensor (ALS) of the smartphone as light intensity detector and its LED flash light as an optical source. An android application "FSense" has been developed which can detect and analyze the fluoride concentration level in water samples. The custom developed application can be used for sharing of in-field sensing data from any remote location to the central water quality monitoring station. We envision that the proposed sensing technique could be useful for initiating a fluoride removal program undertaken by governmental and nongovernmental organizations here in India.

Improving the Sensitivity and Functionality of Mobile Webcam-Based Fluorescence Detectors for Point-of-Care Diagnostics in Global Health

Resource-poor countries and regions require effective, low-cost diagnostic devices for accurate identification and diagnosis of health conditions. Optical detection technologies used for many types of biological and clinical analysis can play a significant role in addressing this need, but must be sufficiently affordable and portable for use in global health settings. Most current clinical optical imaging technologies are accurate and sensitive, but also expensive and difficult to adapt for use in these settings. These challenges can be mitigated by taking advantage of affordable consumer electronics mobile devices such as webcams, mobile phones, charge-coupled device (CCD) cameras, lasers, and LEDs. Low-cost, portable multi-wavelength fluorescence plate readers have been developed for many applications including detection of microbial toxins such as C. Botulinum A neurotoxin, Shiga toxin, and S. aureus enterotoxin B (SEB), and flow cytometry has been used to detect very low cell concentrations. However, the relatively low sensitivities of these devices limit their clinical utility. We have developed several approaches to improve their sensitivity presented here for webcam based fluorescence detectors, including (1) image stacking to improve signal-to-noise ratios; (2) lasers to enable fluorescence excitation for flow cytometry; and (3) streak imaging to capture the trajectory of a single cell, enabling imaging sensors with high noise levels to detect rare cell events. These approaches can also help to overcome some of the limitations of other low-cost optical detection technologies such as CCD or phone-based detectors (like high noise levels or low sensitivities), and provide for their use in low-cost medical diagnostics in resource-poor settings.