Microplastics in the environment: Challenges in analytical chemistry - A review.

Microplastics can be present in the environment as manufactured microplastics (known as primary microplastics) or resulting from the continuous weathering of plastic litter, which yields progressively smaller plastic fragments (known as secondary microplastics). Herein, we discuss the numerous issues associated with the analysis of microplastics, and to a less extent of nanoplastics, in environmental samples (water, sediments, and biological tissues), from their sampling and sample handling to their identification and quantification. The analytical quality control and quality assurance associated with the validation of analytical methods and use of reference materials for the quantification of microplastics are also discussed, as well as the current challenges within this field of research and possible routes to overcome such limitations.

Recent Progress in Biosensors for Environmental Monitoring: A Review.

The environmental monitoring has been one of the priorities at the European and global scale due to the close relationship between the environmental pollution and the human health/socioeconomic development. In this field, the biosensors have been widely employed as cost-effective, fast, in situ, and real-time analytical techniques. The need of portable, rapid, and smart biosensing devices explains the recent development of biosensors with new transduction materials, obtained from nanotechnology, and for multiplexed pollutant detection, involving multidisciplinary experts. This review article provides an update on recent progress in biosensors for the monitoring of air, water, and soil pollutants in real conditions such as pesticides, potentially toxic elements, and small organic molecules including toxins and endocrine disrupting chemicals.

Development of an electrochemical biosensor for alkylphenol detection.

In this work, electrochemical biosensors based on field effect transistors (FET) with single-walled carbon nanotubes (SWCNT) were constructed as disposable analytical devices to detect alkylphenols through immunoreaction using 4-nonylphenol (NP) as model analyte, and validated by comparison with enzyme-linked immunosorbent assay (ELISA). The calibration curve displays a working range with five concentrations between 5 and 500µgL(-1), and for each concentration, five biosensors were analysed for reproducibility estimation and two analytical measurements were performed for each biosensor for repeatability estimation. The accuracy of the biosensors was validated by analyzing NP contents in ten spiked artificial seawater samples and comparing these results to those obtained with the traditional ELISA methodology. Excellent analytical performance was obtained with reproducibility of 0.56±0.08%, repeatability of 0.5±0.2%, limit of detection for NP as low as 5µgL(-1), and average recovery between 97.8% and 104.6%. This work demonstrates that simple biosensors can be used to detect hazardous priority substances in seawater samples, even at low concentrations.

Disposable biosensor for detection of iron (III) in wines.

This paper reports the tuning of a fast, disposable, and label-free biosensor for quantification of iron (III) in food liquid samples such as wine. The biosensor is based on a field effect transistor(FET) where a net work of single-walled carbonnanotubes (SWCNTs) acts as the conductor channel, constituting carbonnanotubes field effect transistors (CNTFETs). An antibody such as transferrin with two specific high-affinity iron (III) binding sites, directly adsorbed to SWCNTs, was used as immunoreaction. Several individual CNTFETs were tested showing a linear range between 0.05 and 2ngmL(-1) and a limit of quantification below 0.05ngmL(-1), much lower than previously reported analytical techniques. The mean coefficient of variation was 0.13% showing a low variability of the analytical response. On the other hand, it was not observed interference effect of zinc (II) ion at least until 1:4 iron-zinc ratio. Finally, recovery percentages of spiked wine samples were around 100%, showing the high accuracy of method. The main advantages of the devices developed are their speed, convenience (it is an economical method), and the avoidance excessive handling samples since they do not require further pre-treatment of samples.

Immunosensors in Clinical Laboratory Diagnostics.

The application of simple, cost-effective, rapid, and accurate diagnostic technologies for detection and identification of cardiac and cancer biomarkers has been a central point in the clinical area. Biosensors have been recognized as efficient alternatives for the diagnostics of various diseases due to their specificity and potential for application on real samples. The role of nanotechnology in the construction of immunological biosensors, that is, immunosensors, has contributed to the improvement of sensitivity, since they are based in the affinity between antibody and antigen. Other analytes than biomarkers such as hormones, pathogenic bacteria, and virus have also been detected by immunosensors for clinical point-of-care applications. In this chapter, we first introduced the various types of immunosensors and discussed their applications in clinical diagnostics over the recent 6 years, mainly as point-of-care technologies for the determination of cardiac and cancer biomarkers, hormones, pathogenic bacteria, and virus. The future perspectives of these devices in the field of clinical diagnostics are also evaluated.

Label-free disposable immunosensor for detection of atrazine.

This work reports the construction of a fast, disposable, and label-free immunosensor for the determination of atrazine. The immunosensor is based on a field effect transistor (FET) where a network of single-walled carbon nanotubes (SWCNTs) acts as the conductor channel, constituting carbon nanotubes field effect transistors (CNTFETs). Anti-atrazine antibodies were adsorbed onto the SWCNTs and subsequently the SWCNTs were protected with Tween 20 to prevent the non-specific binding of bacteria or proteins. The principle of the immunoreaction consists in the direct adsorption of atrazine specific antibodies (anti-atrazine) to SWCNTs networks. After exposed to increasing concentrations of atrazine, the CNTFETs could be used as useful label-free platforms to detect atrazine. Under the optimal conditions, a limit of detection as low as 0.001 ng mL(-1) was obtained, which is lower than that of other methods for the atrazine detection, and in a working range between 0.001 and 10 ng mL(-1). The average recoveries obtained for real water samples spiked with atrazine varied from 87.3% to 108.0%. The results show that the constructed sensors display a high sensitivity and could be useful tools for detecting pesticides like atrazine at low concentrations. They could be also applied to the determination of atrazine in environmental aqueous samples, such as seawater and riverine water.

Critical overview on the application of sensors and biosensors for clinical analysis.

Sensors and biosensors have been increasingly used for clinical analysis due to their miniaturization and portability, allowing the construction of diagnostic devices for point-of-care testing. This paper presents an up-to-date overview and comparison of the analytical performance of sensors and biosensors recently used in clinical analysis. This includes cancer and cardiac biomarkers, hormones, biomolecules, neurotransmitters, bacteria, virus and cancer cells, along with related significant advances since 2011. Some methods of enhancing the analytical performance of sensors and biosensors through their figures of merit are also discussed.

Assessment of cardiovascular disease risk using immunosensors for determination of C-reactive protein levels in serum and saliva: a pilot study.

BACKGROUND: Disposable immunosensors based on field effect transistors with single-walled carbon nanotubes (NTFET) were applied for the first time to clinical samples of undiluted blood serum and saliva for the determination of C-reactive protein (CRP), and validated by comparison with ELISA. RESULTS: The NTFET showed comparable analytical performance with the ELISA when applied to clinical samples, which means that NTFET can be used as an alternative to ELISA. Also, a high correlation between the serum and salivary CRP levels was found with the NTFET, which means that saliva could be used based on a noninvasive sampling as an alternative fluid to blood serum. The establishment of a new range of CRP levels based on saliva was also found. CONCLUSION: The monitoring of CRP in saliva samples by disposable immunosensors could be a valuable approach for the improvement of healthcare services, considering the worldwide increased incidence of cardiovascular diseases.

Disposable immunosensors for C-reactive protein based on carbon nanotubes field effect transistors.

Label-free immunosensors based on single-walled carbon nanotubes field effect transistor (NTFET) devices were developed for the detection of C-reactive protein (CRP) which is currently the best validated inflammatory biomarker associated with cardiovascular diseases. The immunoreaction principle consists in the direct adsorption of CRP specific antibodies (anti-CRP) to single-walled carbon nanotubes (SWCNTs) networks. Such anti-CRP are the molecular receptors of CRP antigens which, in turn, can be detected by the developed NTFET devices in a linear dynamic range of 10(-4)-10(2) µg/mL. Thus, typical values of CRP (in blood serum) for healthy persons (<1 µg/mL), and higher levels (>5 µg/mL) corresponding to pathological states, can be both detected with the NTFET immunosensors, becoming an advantageous alternative as the basis for the development of analytical instrumentation for assessment of risk of occurrence of cardiovascular diseases. A log-log linear regression was applied to the experimental data with a correlation coefficient of r=0.9962 (p<0.001), and there is no statistical difference (from ANOVA) between individual NTFET devices (p=0.9582), demonstrating acceptable reproducibility. According to the experimental results, the estimate of detection limit (LOD, 10(-4)µg/mL) is 3-fold lower than that of some conventional immunoassay techniques for blood serum (e.g., LOD of 0.2 µg/mL for high-sensitivity enzyme-linked immunosorbent assay), and the dynamic range (10(-4)-10(2)µg/mL) is about 6-fold higher. Furthermore, this simple and low-cost methodology allows the use of sample volumes as low as 1 µL for the label-free detection of CRP.

Removal of the organic content from a bleached kraft pulp mill effluent by a treatment with silica-alginate-fungi biocomposites.

This study attempts a treatment strategy of a bleached kraft pulp mill effluent with Rhizopus oryzae or Pleurotus sajor caju encapsulated on silica-alginate (biocomposite of silica-alginate-fungi, with the purpose of reducing its potential impact in the environment. Active (alive) or inactive (death by sterilization) Rhizopus oryzae or Pleurotus sajor caju was encapsulated in alginate beads. Five beads containing active and inactive fungus were placed in a mold and filled with silica hydrogel (biocomposites). The biocomposites were added to batch reactors containing the bleached kraft pulp mill effluent. The treatment of bleached kraft pulp mill effluent by active and inactive biocomposites was performed throughout 29 days at 28°C. The efficiency of treatment was evaluated by measuring the removal of organic compounds, chemical oxygen demand and the relative absorbance ratio over time. Both fungi species showed potential for removal of organic compounds, colour and chemical oxygen demand. Maximum values of reduction in terms of colour (56%), chemical oxygen demand (65%) and organic compounds (72-79%) were attained after 29 days of treatment of bleached kraft pulp mill effluent by active Rhizopus oryzae biocomposites. The immobilization of fungi, the need for low fungal biomass, and the possibility of reutlization of the biocomposites clearly demonstrate the industrial and environmental interest in bleached kraft pulp mill effluent treatment by silica-alginate-fungi biocomposites.

Strategies for enhancing the analytical performance of nanomaterial-based sensors.

We provide a state-of-the-art review of the main strategies for the enhancement of analytical performance of sensors using nanomaterials, particularly nanowires and carbon-based materials. We emphasize the way to overcome the problem of device-to-device variation. We discuss the study of the influence of nanomaterial characteristics, sensor dimensions and operational conditions on sensing performance, and the application of appropriate calibration models.

Screening of single-walled carbon nanotubes by optical fiber sensing.

A methodology based on optical fiber (OF) sensing was developed to screen single walled carbon nanotubes (SWCNT) in aqueous solutions. This method was validated by the comparison of its analytical performance with that of an ultraviolet-visible (UV-Vis) technique by monitoring the absorbance intensities at 500 nm, and no significant difference (p=0.854) was observed between such two methods. The results obtained by the OF sensor were encouraging in what concerns a new approach for detection and quantification of SWCNT in solutions due to its compact design, less expensive materials and equipment, as well as a requirement of low volume of sample. Additionally, it was concluded that the nonlinear calibration model observed for the analytical response with the OF probe follows the general cumulative symmetric double sigmoidal (SDS) model (R(2)=0.9999), once adapted for the analytical region of interest.

Olive oil mill wastewaters before and after treatment: a critical review from the ecotoxicological point of view.

The olive oil mill wastewater (OMW) is a problematic and polluting effluent which may degrade the soil and water quality, with critical negative impacts on ecosystems functions and services provided. The main purpose of this review paper is presenting the state of the art of OMW treatments focusing on their efficiency to reduce OMW toxicity, and emphasizing the role of ecotoxicological tests on the evaluation of such efficiency before the up-scale of treatment methodologies being considered. In the majority of research works, the reduction of OMW toxicity is related to the degradation of phenolic compounds (considered as the main responsible for the toxic effects of OMW on seed germination, on bacteria, and on different species of soil and aquatic invertebrates) or the decrease of chemical oxygen demand content, which is not scientifically sound. Batteries of ecotoxicological tests are not applied before and after OMW treatments as they should be, thus leading to knowledge gaps in terms of accurate and real assessment of OMW toxicity. Although the toxicity of OMW is usually high, the evaluation of effects on sub-lethal endpoints, on individual and multispecies test systems, are currently lacking, and the real impacts yielded by its dilution, in freshwater trophic chains of receiving systems can not be assessed. As far as the terrestrial compartment is considered, ecotoxicological data available include tests only with plants and the evaluation of soil microbial parameters, reflecting concerns with the impacts on crops when using OMW for irrigation purposes. The evaluation of its ecotoxicity to other edaphic species were not performed giving rise to a completely lack of knowledge about the consequences of such practice on other soil functions. OMW production is a great environmental problem in Mediterranean countries; hence, engineers, chemists and ecotoxicologists should face this problem together to find an ecologically friend solution.

Optical fiber based methodology for assessment of thiocyanate in seawater.

A new methodology for the assessment of thiocyanate (SCN(-)) is proposed based on optical fiber (OF) detection coupled to a liquid chromatography system (LC). The developed methodology showed an adequate performance for the analysis of SCN(-) comparable to a high performance liquid chromatography with UV detector (HPLC-UV) methodology: a detection limit of 3 µg L(-1), a linear range from 4 to 400 µg L(-1), and an analytical time of less than 6 min. The OF based methodology was of compact design and easy operation. This simple system has the potential to be used as a sensing approach for SCN(-) in seawater.