Milk and dairy products have high nutritional value and their consumption contributes to a balanced and nutritious diet. Cow milk is more allergenic than the milk from other species and therefore adulteration of these milks with cow milk can pose a serious threat to consumers [1]. To detect milk adulteration, several methods have been employed which, however, cannot be performed at the point of need. On the other hand, biosensors can provide fast and quantitative on-site determinations [2]. In this work, a silicon-based photonic dip-stick immunosensor, which includes two U-shaped Mach-Zehnder Interferometers (MZIs), was employed for the detection of ewe, goat and donkey milk adulteration with cow milk. The sensing windows of the two MZIs are located to one end of the chip allowing its immersion directly into the sample and the light input and output ports are located at the other end of the chip which is connected through a bifurcated optical fiber to white light source and a spectrophotometer. The transmission spectrum of both MZIs is subjected to Fourier transform to distinguish and monitor in real-time the phase shifts due to bioreactions taking place onto the sensing windows of the two MZIs. For detection of milk adulteration, the sensing arm of one of the MZIs is modified with bovine k-casein and the other with blocking protein to serve as reference. A competitive immunoassay format was followed where the chip was first immersed in a mixture of 50-times diluted milk with a rabbit anti-k-casein antibody solution for 5 min, followed by 5-min immersion in a secondary antibody solution. Limit of detections of 0.05 and 0.1% cow milk in ewe/goat and donkey milk, respectively, were achieved for a total assay time of 12 min. Thus, this fast, sensitive, and simple assay is ideal for on-site detection of milk adulteration.

References:

1. H. Montgomery, S.A. Haughey, C.T. Elliott, Glob. Food Sec. 26 (2020) 100447.
2. M. Nehra, M. Lettieri, N. Dilbaghi, S. Kumar, G. Marrazza, Sensors 20 (2020) 32.

Acknowledgment: This research has been co‐financed by the European Regional Development Fund of the European Union and Greek national funds through the Operational Program Competitiveness, Entrepreneurship and Innovation, under the call RESEARCH–CREATE–INNOVATE (project code: Τ2ΕΔΚ-01934 FOODSENS).

Nanostructured surfaces of noble metals enhance considerably the intensity of photoluminescence from molecules immobilized on them providing a mean for their sensitive detection. The combination of such surfaces with immunochemical techniques provides assays that are characterized by high sensitivity and specificity. Thus, the aim of this work was to fabricate and evaluate nanostructured silver surfaces as substrates for the immunochemical detection of two ovarian cancer markers, carbohydrate antigen 125 (Ca125) and human epididymis protein 4 (HE4). The substrates were prepared following a metal-assisted chemical etching procedure on silicon wafers resulting in the creation of silicon nanowires decorated with either silver dendrites or silver nanoparticles. Non-competitive immunoassays for detection of the biomarkers were developed on these substrates using pairs of highly specific mouse monoclonal antibodies; one as capture and the other as detection. The detection antibodies were biotinylated to allow detection of immunocomplexes through reaction with streptavidin labeled with fluorescent labels for photoluminescence measurements. The measurements were performed employing an in-house developed low-cost optical set-up. It was found that, the higher signals were received using substrates with silver dendrites rather than with silver nanoparticles. The detection limits achieved for Ca125 and HE4 were 10 U/mL and 0.3 ng/mL, respectively, and the linear dynamic ranges extended up to 200 U/mL for Ca125 and 2.5 ng/mL for HE4, covering the required clinical concentration ranges. The nanostructured silver surfaces are currently evaluated as substrates for the development of multi-analyte assays targeting both ovarian cancer markers.

Pathogens can be detected electrochemically by measuring guanine oxidation signals generated from RNA or DNA hybridized to a biosensor working electrode. However the associated limit of detection (LOD) is not sufficiently low for widespread clinical use. Working electrodes employing nanomaterials such as carbon nanotubes successfully reduce the LOD but nanosensors experience high variability, poor fabrication yield and high production cost. This work demonstrates a new approach for electrochemically detecting pathogens and antimicrobial resistance genes that shifts the guanine oxidation source from naturally occurring RNA to synthetic oligonucleotides. Signal amplification is accomplished by binding RNA from lysed cells to microparticles conjugated with millions of guanine-rich oligonucleotide tags. A sandwich hybridization assay binds RNA between a screen printed carbon working electrode conjugated with recognition probes and a microparticle conjugated with electrochemical oligonucleotide tags. The tags contain a polyguanine detection sequence and an RNA capture sequence on the same oligonucleotide. Single stranded polyguanine is prefabricated into a quadruplex to enable 8-oxoguanine signals at 0.47V, which eliminates nonspecific guanine oxidation signals from the RNA while further reducing LOD over guanine oxidation. A 70 mer capture sequence was found to be more selective and hybridize faster at room temperature than conventional 20 mer capture sequences. Particle sizes were evaluated from 100 nm to 3 µm in diameter, and the larger diameter particles produced a greater detection signal. Better performance was obtained with magnetic microparticles which allowed magnetic separation of target RNA from nonspecific materials. The high density magnetic microparticles rested on the electrode surface causing a portion of the oligonucleotides to adsorb to the working electrode surface.

Ag/TiO₂ Nanocomposites for Nanothermometry in biological environment

Local temperature determination is essential to understand heat transport phenomena at the nanoscale and to design nanodevices for biomedical, photonic and optoelectronic applications [1]. In particular, with the emergence of photothermal therapy for the local treatment of cancerous tissues, the availability of nanothermometric techniques with high spatial resolution capable of remotely determining and modifying the intracellular temperature has become necessary. From this point of view, Raman spectroscopy is adequate for the purpose: the ratio between the intensity of the anti-Stokes and Stokes signals of a specific normal mode of vibration of an active Raman material, in fact, follows the Boltzmann distribution, linked to the temperature local. Titanium dioxide can be used as an optical material for temperature detection in biological samples, due to its high biocompatibility, already demonstrated in the literature [2], and to its strong Raman scattering signal. Moreover, the realisation of composite nanomaterials containing a metal and a Raman active material opens the way to their use in the field of photothermal therapy. The metal, silver nanoparticles, may act simultaneously as a nanoheater and as a plasmonic substrate, while anatase acts as a Raman nanothermometer [3].

In the present work, nanoparticles consisting of an Ag core, covered by a TiO₂ shell, Ag@TiO₂ core-shell, are suitably synthesised through a one-pot method. Silver nanoparticles synthesised in DMF are coated by controlled hydrolysis of titanium tetrabutoxide in the same reaction environment [4,5]. The synthesis led to nanocomposites where AgNPs are covered by a diffuse layer of anatase.

The nanocomposites are characterized by UV/Vis spectroscopy, Dynamic Light Scattering (DLS), X-Ray Diffraction (XRD), High Resolution Transmission Electronic Microscopy (HRTEM) and Raman spectroscopy. The samples obtained proved to be good Raman nanothermometers with a sensitivity superior to that of simple anatase nanoparticles. In particular, they showed maximum efficiency working at an excitation wavelength of 800 nm.

1. Bradac, C.; Lim, S.F.; Chang, H.-C.; Aharonovich I. Optical Nanoscale Thermometry: From Fundamental Mechanisms to Emerging Practical Applications. Optical Mater. 2020, 8, 200018.3. https://doi.org/10.1002/adom.202000183.
2. Yin, Z.F.; Wu, L.; Yang, H.G.; Su, Y.H. Yin, Z.F.; Wu, L.; Yang, H.G.; Su, Y.H. PCCP, 2013 , 15, 14, 4844. PCCP, 2013, 15, 14, 4844. https://doi.org/10.1039/c3cp43938k.
3. Zani, V.; Pedron, D.; Pilot, R.; Signorini, R. Contactless Temperature Sensing at the Microscale Based on Titanium Dioxide Raman Thermometry. Biosensors 2021, 11 (4). https://doi.org/10.3390/bios11040102.
4. Pastoriza-Santos, I.; Koktysh, D.; Mamedov, A.; Giersig, M.; Kotov N.; Liz-Marzán, L. One-Pot Synthesis of Ag@TiO2 Core-Shell Nanoparticles and Their Layer-by-Layer Assembly. Langmuir, 2000, 16, 2731-2735. https://doi.org/10.1021/la991212g.
5. Wang, P.; Wang, D.; Xie, T.; Li, H.; Yang M.; Wei, X. Preparation of monodisperse Ag/Anatase TiO2 core–shell nanoparticles. Materials Chemistry and Physics, 2008, 109, 108-183. https://doi.org/10.1016/j.matchemphys.2007.11.019

Digital tools are notoriously able to assist designers in solving several issues with high accuracy and minimized computational efforts. In this sense, maximization of human comfort in the built environment is a target for various design procedures, where mathematical models and standardized protocols are generally used for well-being purposes. In this paper, a selection of recent experimental studies and pilot studies in which various artificial intelligence tools and wearable or smartphone-based sensors are used to support a rapid and efficient body motion analysis are used to support and assess a multi-criteria human comfort-driven design approach for various structural building components and configurations of technical interest. The so-called “emotional architecture” and its correlated nervous feelings, as well as human reactions and behaviours, which are intrinsic part of the issue, are quantitatively measured and compared to find possible feedback in structural design optimization. Major modification in human behaviours can result in relevant changes of body motion features, and thus in corresponding reaction forces, loading conditions, operational configurations for structural components and systems, etc. Both remote digital technologies based on artificial intelligence and facial micro-expression analysis, as well as multiple wearable or smartphone-based sensors are used for in-field experiments, to capture kinematic and biometric parameters of volunteers moving in various structural environments, are summarized in this paper. Trends and challenges of these applications are discussed with practical examples.

This study aims to create a fluorescence-based measurement system to enable the development of miniaturized and low-cost optical biosensors. Alternative to bulky and expensive optical equipment, a custom-made 3D-printed setup was designed and modeled for electrical detection and monitoring of the fluorescence light intensity. The system comprises a blue LED (450 nm) and a photodiode (PD) mounted orthogonally on the top and back of the cell package. The LED is used to optically excite the fluorescent dye particles in a solution, resulting in a fluorescence light that is captured by the PD, yielding a measurable electrical current proportional to the light intensity. This system was used to explore the ratiometric fluorescence quenching of the fluorescent dye Bodipy in the presence of the quencher o-BBV to develop a novel non-enzyme-based glucose sensing platform. The fluorescence quenching of the boron-dipyrromethene (Bodipy) solution was initiated by exposing the mixture of Bodipy (2x10^-6 M) and boronic acid conjugated viologen (o-BBV) (2x10^-3 M) to UV light for 120 seconds. Monitoring the fluorescence intensities of the solutions were performed at various pHs (5.5, 7.4 and 8.0) and temperatures (0°C, 4°C, 25°C, and 37°C) before and after the addition of glucose (30 mM). The results showed that the emission intensity of the Bodipy solution was recovered after the addition of glucose, making it a potential platform for glucose sensing. The measured photodiode current in the developed system is found to be coherent with the intensity of the Bodipy emission measured by the fluorescent spectrometer of the same solution. The advantage of our system is that is possible to measure concentrated samples, whereas a fluorescent spectrometer requires only working with diluted samples. This study provides a proof-of-concept demonstration for a low-cost and miniaturized optical biosensor, offering the potential for further development and optimization.

In the last years, flexible electronics have suffer a massive growth as a response to the high demand of new skin patch sensor devices targeted for personnel health monitoring. In this context, the incorporation of biological polymers in the backbone of these soft systems brings new opportunities in terms of biocompatibility and sustainability performance. However, the suitable integration of a conductive patterned material is still a challenge in order to achieve good adhesion and high transparency. Thus, silver nanowires (AgNWs) constitute promising candidates for the fabrication of flexible transparent conductive films. Herein, a chitosan membrane doped with a plasticizer element was made conductive, through a one-step process, by using an optimized ratio of chitosan-lactic acid-AgNWs dispersion. This formulation was applied by screen printing technique and the influence of polymer ratio, cure temperature and number of layers applied with the AgNW-based ink was investigated. Compared to the conventional water-based AgNW dispersions, the here proposed chitosan-doped ink enabled the fabrication of transparent electrode platforms holding good stability, homogeneity and electrical features.

Per- and polyfluoroalkyl compounds (PFAS) are synthetic compounds recently classified as permanent and emerging chemicals, since their bioaccumulation in human and environment. Among the PFAS compounds, perfluorooctanoic acid (PFOA) are based on carbon-fluorine functional groups, which have been demonstrated resistant to degradation. Recent work on the accurate detection of PFOA in the range of 1.1 and 3.4 ng/mL in biological samples (plasma) uses the conventional HPLC/HRMS technique [1]. For the environmental concern, the level of PFOA in rainwater has been demonstrated to exceed the limits of EPA guidelines Here, PFOA concentrations were detected between 12.6 ng/L and 287 ng/L by UPLC-MS/MS [2]. Although HPLC/HRMS still remains an accurate analytical method able to detect a wide range of analytes, it suffers from practical drawbacks, high costs, user experiences in data treatment and interpretation, and so on. So, alternative methods in PFOA detection with addressed high sensitivity, simple operation, fast response time and transportability are currently gaining attention in research. In particular, the design of novel screening tools for the selective and sensitive quantification of PFAS compounds in water is highly desirable. Electrochemical sensors have been recently proposed for PFOA quantification in water [3,4], some of which reported the application of molecularly imprinted polymers (MIP) to selectively discriminate the analyte from matrix interferences.
MIP relies on artificial synthetic polymeric receptors intensively used in sensor development for water monitoring. Those are prepared through different synthetic techniques, in the presence of a polymerisation mixture comprising functional monomers and cross-linker agents that surround the analyte target complementary to its functionalities. Selective cavities are then formed onto a polymeric backbone through elution processes. In this work, we report a preliminary result on the solid-phase synthesis of MIPs in the form of nanoparticles (<150 nm) applied in sensor development for the highly sensitive and selective quantification of PFAS in water.
The solid phase polymerisation was carried out starting from an already available protocol [5] using silanized glass beads to selectively orientate the PFOA target. A polymerisation mixture was prepared by adding the functional monomers (itaconic acid, 2-hydroxyethyl methacrylate) and cross-linker agents. Here, a redox mediator, e.g. ferrocene methyl methacrylate was added to label a redox mediator to the high affinity nanoparticles. Finally, the UV-light polymerisation was carried out. To elute the target, a protocol involving several steps of temperature change was used, to finally elute the high affinity nanoMIP. The developed nanoparticles were characterised by dynamic light scattering (DLS), showing a size of 138 nm with a polydispersity index (PDI) below 0.3.
During sensor development, functionalized screen-printed platinum electrodes (SPPtE) and the nanoMIPs have been used as the transduction and the receptor element, respectively. Functionalization of SPPtE was optimised by using 0.5 % of APTES to be activated during nanoMIPs immobilization. The same were immobilised through EDC/NHS chemistry coupling. Each step of electrode modification was monitored by electrochemical methods, such as the cyclic voltammetry and differential pulse voltammetry. Results from CV/DPV measurement presented a reversible redox reaction due to the presence of the redox labelled nanoMIPs, that further facilitated the transferring of electrons from solution to the electrode surface. The developed sensors have been tested towards increasing concentration (1.5 – 100 ng/mL) of PFAS dissolved in PBS (50 mM pH 7.4), showing highly sensitive properties of the developed nanoMIPs. Optimisation and quality properties of the developed sensors, such as the selectivity and stability, are ongoing to be studied.

Background and aims: Non-Invasive blood glucose monitoring using infrared (IR) light is considered a handy and reliable tool to measure blood sugar levels during daily activities. IR-based glucose monitoring principle depends on the variant absorption levels of IR light wave by blood with high or low levels of glucose solution. This paper introduces a low-cost finger probe to measure glucose based on Arduino and machine learning-based Clark error grids.

Methods: An electronic blood glucose meter is designed and implemented in a non-invasive and painless manner based on an infrared sensor. The electrical signal expressing the level of glucose in the blood with a mathematical equation is used for calibration and mapping the physical and electrical values. The final numerical value is validated with the Clark error grid by implementing fuzzy logic (FL).

Results: The designed device is tested on 30 subjects with 15 diabetes subjects. The results show a high significance of results with less than 3% of error with the reference device. The proposed method of using FL with Clark error grid gives more confident and precise output in this kind of portable device.

A novel simple optical sensor based on fast protein liquid chromatograph (FPLC) was developed and tested for monitoring end stage renal disease (ESRD) patients on continuous ambulatory peritoneal dialysis (CAPD). The device provides direct determination of proteins and lower molecular weight metabolites in effluent peritoneal dialysate using low-cost PD-10 columns and photometric detection at the wavelengths 285 nm or 260 nm with deep ultraviolet light-emitting diodes (UV LED).
The sensor was calibrated with bovine serum albumin (BSA), adenosine triphosphate (ATP), inosine monophosphate (IMP), inosine (Ino), and hypoxanthine (Hx) standard solutions. Chromatograms of effluent peritoneal dialysate taken from 28 ESRD patients were processed and approximated by a set of split-Gaussian functions; UV absorption spectra of the samples were recorded in parallel.
All chromatograms show three overlapping peaks: the first one represents proteins; the other two peaks probably correspond to mid- and low molecular weight metabolites. Strong correlation (R2 = 0,947) was reveled between the area of the first peak and total protein (TP) concentration determined by a standard biochemical assay, this makes possible estimation of peritoneal protein loss with a reasonable precision less than 15%.
The elution time of the second peak was close the elution time of IMP (M=348 Da). The area of the second peak correlated relatively weakly with dialysate optical density at a wavelength 355-365 nm, associated with the UV absorption of advanced glycation end (AGE) products, but there is still not enough evidence to attribute confidently this peak to AGE. The third peak showed the elution time close to Hx (M=136 Da), the area of this peak correlated with the optical density of the eluate at a wavelength 255-265 nm, associated with the UV absorption of purines and pyrimidines.
Thus, we demonstrated the possibility of estimation of proteins and lower molecular weight metabolites in effluent peritoneal dialysate with the compact and affordable chromatographic optical sensor.