Microplastic pollution in water bodies is an alarming problem which needs to be addressed. However, issues such as size, shape and their appearance to light (transparent or translucent) make it difficult to be optically detected. Here, a feasibility study of a portable prototype optical sensor with the capability of measuring simultaneously specular laser light reflection and transmission from microplastic particles is presented. The specular reflection signal and the transmitted interference pattern were recorded with a photodiode and a CCD camera, respectively. With the combination of these two modes of detection, it is possible to screen the type, size, and nonplanarity of two microplastics types, i.e., transparent polyethylene terephthalate (PET) and translucent low-density polyethylene (LDPE), in a volume of freshwater, with high confidence. In principle, the prototype could be used for the detection of both floating microplastics as well as microplastics experiencing sedimentation in natural water bodies, and in water filtration in water treatment plants.

Erosion of microplastics due to residence time in aquatic environments causes roughening of the microplastic. Unfortunately, currently used measurement methods do not provide information on the surface roughness of the microplastic embedded in water. In this study we propose a novel method by using transmittance to get information on the magnitude of the surface roughness of microplastics and to rank microplastics by thickness. For such a purpose, we studied optical properties such as dispersion, absorption of both plastics and water in the partial spectral range of visible light (Vis), transmission and scattering of light by plastic sheets, as well as, the calculated sample thickness in the Vis region. These were explored for the detection of both smooth and roughened plastic sheets immersed in water. Moreover, by using the transmission spectrum and refractive index of both plastic and water it is possible to estimate the average surface roughness of plastic samples. Our results suggest that the optical properties in the Vis region offer an interesting way for the detection of both rough and smooth plastic sheets and for ranking the type of plastics in an aquatic environment.

Due to the proven carcinogenicity of Sudan III and IV dyes, they are considered global public health issues. They are banned in all forms as food colourants. We propose the monitoring of simple and easy-to-measure optical properties of palm oils, such as the refractive indices and spectrophotometric properties, as efficient indicators to detect adulteration. Coupling these results with principal component analysis, excess refractive index, and integration of transmittance introduces a novel detection tool for the authentication of edible palm oil. This opens a new opportunity for accurate handheld devices to detect adulteration and provide control in the field. This work assessed in total of 49 samples, some collected from different parts of Ghana and others, in-house adulterated samples. The Ghana Food and Drugs Authority, who performed a complex and expensive chemical analysis of the samples, confirmed our results with good agreement.

Liquid fuel adulteration has several far-reaching impacts such as environmental pollution. A widespread practice is typically the adulteration of diesel oil by kerosene. The relatively cheap price of kerosene is probably the most important reason for its usage in illegal adulteration. Herein, we demonstrate the use of a prototype optical sensor for efficient tracking of adulterated diesel oil. In this study, a prototype of an optical sensor for screening of fake diesel oil is proposed. The device exploits the phenomenon of laser light reflection from a fuel film over a roughened glass plate. The sensing mechanism of the devise is based on the refractive index mismatch between the glass and the fuel sample, and the wetting property of the fuel film over the roughened surface. For the sake of comparison, the refractive index for each of the fuel samples was measured at room temperature with the aid of an automatic temperature controlled Abbe table refractometer. The sensitivity of this prototype optical sensor was tested using training sets of diesel oil samples adulterated with low concentrations of kerosene. Originally, a commercial handheld glossmeter, with a new innovation of a removable sensor head for liquid inspection is presented as a prototype sensor for the screening of possible adulteration of diesel oils with kerosene. The significant difference in the signal readings obtained from carefully prepared training sets of adulterated diesel oil composed of low percentages (5–15%) of kerosene has proven the high sensitivity of the developed sensor. The ability to detect low concentrations of kerosene in diesel using the newly developed hand-held prototype sensor proves its high sensitivity compared to a high-accuracy Abbe refractometer. We envisage that this proposed sensor could, in the future, be made accessible to the authorities as a mobile fake fuel measurement unit.

The knowledge of the plastic type, thickness, and the nature of the surface is important towards the monitoring of microplastic pollution in water bodies, especially when vis-NIR spectroscopy is utilized. Factors such as complex environment and surface roughness induced-light scattering of the probing light limit the optical detection of these parameters in in-situ measurements, however. In this paper, a novel application of Kramers–Kronig analysis was exploited to identify both smooth and rough film-type macroplastics with unknown thickness. This method is particularly useful in the in-situ identification of unknown film-like macroplastics; although the sample is large, the ratio function is detected from an area that corresponds to the size of a MP. Therefore, it can be applied for the case of large size MPs. The validity of the method was demonstrated using transmittance data for smooth and roughened plastics given in Kanyathare et al., 2020.