Adnane Abdelghani

Volatile Organic Compounds (VOCs) are important indicators of environmental pollution and metabolic activity, making their sensitive and selective detection highly relevant for applications in health monitoring and air quality assessment. Graphene, owing to its exceptional charge transport properties, large surface area, and tunable surface chemistry, is a promising candidate for advanced gas and VOCs sensing. Here we report chemoresistive sensors based on pristine graphene and graphene decorated with platinum (Pt), palladium (Pd), and gold (Au) nanoparticles toward both aromatic (benzene, toluene, and xylene) and non-aromatic (ethanol, methanol, and acetone) vapor compound detection. The detection is achieved at room temperature, and the results demonstrate that graphene functionalized with noble metal nanoparticles shows significant enhancements in sensitivity compared to pristine graphene, mainly against ethanol, toluene and xylene vapors for the Au–graphene sensors. A comparative study with Multi-Walled Carbon Nanotube (MWCNT) sensors decorated with the same type of nanoparticles revealed clear advantages of graphene, attributed to the microstructure and porous structure of graphene powders, which facilitate efficient charge transfer upon vapor adsorption.

Many research works report a sensitive detection of a wide variety of gas species. However, their in-lab detection is usually performed by using single gases and, therefore, selectivity often remains an unsolved issue. This paper reports a four-sensor array employing different nano-carbon sensitive layers (bare graphene, SnO ₂ @Graphene, WO ₃ @Graphene, and Au@CNTs). The different gas-sensitive films were characterised via several techniques such as FESEM, TEM, and Raman. First, an extensive study was performed to detect isolated NO ₂ , CO ₂ , and NH ₃ molecules, unravelling the sensing mechanism at the operating temperatures applied. Besides, the effect of the ambient moisture was also evaluated. Afterwards, a model for target gas identification and concentration prediction was developed. Indeed, the sensor array was used in mixtures of NO ₂ and CO ₂ for studying the cross-sensitivity and developing a calibration model. As a result, the NO ₂ detection with different background levels of CO ₂ was achieved with an R ² of 0.987 and an RMSE of about 22 ppb.

Thousands of gas molecules are expelled in exhaled breath, and some of them can reveal diseases and metabolomic disorders. For that reason, the development of fast, inexpensive, and reliable sensing devices has been attracting growing interest. Here, we present the development of different chemoresistors based on multi-walled carbon nanotubes (MWCNTs) decorated with platinum (MWCNT/Pt) and palladium (MWCNT/Pt) nanoparticles and also functionalized with a self-assembled monolayer (SAM) of 11-amino-1-undecanethiol (Thiol-amine). The nanocomposites developed are a proof-of-concept to detect some biomarker molecules. Specifically, the capability to identify and measure different concentrations of volatile organic compounds (VOCs), either aromatic (toluene and benzene) and non-aromatic (ethanol and methanol) was assessed. As a result, this paper reports the significant differences in sensing performance achieved according to the metal nanoparticle used, and the high sensitivity obtained when SAMs are grown on the sensitive film, acting as a receptor for biomarker vapours.

Food is a means to sustain and enjoy life, but it is also a medium for microbial contamination, causing disease and death. Fruits, vegetables, meat, and water are the common sources of contamination. Escherichia coli is one of the most frequent Pathogenic Bacteria responsible for food poisoning and food-related infections. E. coli infection causes severe bloody diarrhea, abdominal cramps, and occasional vomiting. In the present study, electrochemical impedance spectroscopy (EIS), surface plasmon resonance (SPR), and physisorption techniques were evaluated to decrease sample preparation time and to improve the sensitivity and specificity for the detection of low levels of pathogenic Escherichia coli in frozen chicken meat. The electrical and optical properties of the immobilized anti-E. coli antibody were studied. Moreover, the developed biosensor was used for E. coli detection in inoculated frozen chicken meat.

Benzene, toluene, and xylene, commonly known as BTX, are hazardous aromatic organic vapors with high toxicity towards living organisms. Many techniques are being developed to provide the community with portable, cost effective, and high performance BTX sensing devices in order to effectively monitor the quality of air. In this paper, we study the effect of decorating graphene with tin oxide (SnO₂) or tungsten oxide (WO₃) nanoparticles on its performance as a chemoresistive material for detecting BTX vapors. Transmission electron microscopy and environmental scanning electron microscopy are used as morphological characterization techniques. SnO₂-decorated graphene displayed high sensitivity towards benzene, toluene, and xylene with the lowest tested concentrations of 2 ppm, 1.5 ppm, and 0.2 ppm, respectively. In addition, we found that, by employing these nanomaterials, the observed response could provide a unique double signal confirmation to identify the presence of benzene vapors for monitoring occupational exposure in the textiles, painting, and adhesives industries or in fuel stations.

Aromatic volatile organic compound (VOC) sensors are attracting growing interest as a response to the pressing market need for sensitive, fast response, low power consumption and stable sensors. Benzene and toluene detection is subject to several potential applications such as air monitoring in chemical industries or even biosensing of human breath. In this work, we report the fabrication of a room temperature toluene and benzene sensor based on multiwall carbon nanotubes (MWCNTs) decorated with gold nanoparticles and functionalised with a long-chain thiol self-assembled monolayer, 1-hexadecanethiol (HDT). High-resolution transmission electron microscopy (HRTEM) and Fourier transform infrared spectroscopy (FTIR) were performed to characterize the gold nanoparticle decoration and to examine the thiol monolayer bonding to the MWCNTs. The detection of aromatic vapours using Au-MWCNT and HDT/Au-MWCNT sensors down to the ppm range shows that the presence of the self-assembled layer increases the sensitivity (up to 17 times), selectivity and improves the response dynamics of the sensors.

Electrochemical immunosensors are generally layer‐by‐layer or sandwich systems designed to detect an analyte in a solution. Immunosensors are mainly based on the high affinity and specificity of the antibody towards its antigen. This work aims to answer the following question: if we ‘flip’ the immunosensor and build it backwards, thus detecting the antibody with the antigen instead of detecting the antigen with the antibody, will we obtain the same immunosensors properties or not? To answer this question, they tested a system composed of glycated human serum albumin and antibody‐functionalised gold nanoparticles. Impedance spectrum results showed a difference in both the sensitivity and linear range of the built impedimetric immunosensors. The sensitivity of the sensor using the antibody as a bioreceptor was approximated to 0.32 [%. [% (Glycated to total albumin])] − 1] against a sensitivity of 0.80 [%. [% (Glycated to total albumin])] − 1] for the ‘upside‐down’ sensor, using the antigen as a bioreceptor. This study observed also a shift to high glycation levels in the linear range of the upside‐down sensor. These differences could be explained by the effect of steric hindrance and a higher degree of freedom allowing better characteristics for the upside‐down immunosensor.

Escherichia coli is an important pollution indicator and is the most important foodborne pathogens of public health concern. The chicken meat is one of the most important sources of good quality protein, and it is also susceptible to microbial contamination and often implicated in foodborne disease. In such context, the detection of E. coli K12 in frozen chicken meat was investigated by electrochemical impedance spectroscopy and surface plasmon resonance imaging techniques. The anti‐E. coli antibody was first immobilized onto gold surface by physisorption technique. The electrical and optical properties of the immobilized anti‐E. coli K12 antibody were studied. The binding of the E. coli K12 bacteria with the anti‐E. coli antibody layer was measured with a detection limit of 10³ cfu/ml. This detection limit is better than those obtained with the enzyme‐linked immunosorbent assay (ELISA) technique. Moreover, the developed biosensor was used for E. coli K12 detection in inoculated frozen chicken meat.Practical applications: Escherichia coli is an important pollution indicator and is the most important foodborne pathogens of public health concern. The present study deals with the development of bacteria biosensors based on electrochemical impedance spectroscopy and surface plasmon resonance imaging techniques for E. coli K12 detection in inoculated frozen chicken meat. A detection limit of 10³ cfu/ml was obtained with the developed biosensors that was better than those obtained with classical methods such as ELISA (enzyme‐linked immunosorbent assay). This research work opens tremendous potential applications for the detection of pathogens in food at the early stage particularly with the development of miniaturized multiarrays platform based on impedance spectroscopy.

Iron oxide (Fe₂O₃) thin films were deposited on glass substrate by varying substrate temperature (T_s) from 300 to 450°C using spray pyrolysis technique. The effect of T_s on the physical properties of Fe₂O₃ layers was studied. The XRD spectra reveal the formation of α-Fe₂O₃. The best crystallinity is obtained at T_s = 400°C. Optical analysis allows us to know that α–Fe₂O₃ thin films displayed a band gap from 2.07 to 2.16 eV for direct transition and from 1.67 to 2 eV for indirect transition. The maximum value of Hall mobility (µ = 62cm².V⁻¹. s⁻¹) is obtained at T_s = 400°C. Hence, the obtained result of gas sensing proves that α-Fe₂O₃ has good sensitivity and stability at operating temperature equal to 300°C. Besides, CuO/α-Fe₂O₃/ZnO has a photovoltaic effect. That the open circuit voltage (V_oc) and short circuit current density (J_sc) are equal to 0.5 V and 0.43 mA/cm² respectively.