Carbon-based quantum particles, especially spherical carbon quantum dots (CQDs) and nanosheets like graphene quantum dots (GQDs), are an emerging class of quantum dots with unique properties owing to their quantum confinement effect.

Bacterial infections remain one of the principal causes of morbidity and mortality worldwide. The number of deaths due to infections is declining every year by only 1% with a forecast of 13 million deaths in 2050. Among the 1400 recognized human pathogens, the majority of infectious diseases is caused by just a few, about 20 pathogens only. While the development of vaccinations and novel antibacterial drugs and treatments are at the forefront of research, and strongly financially supported by policy makers, another manner to limit and control infectious outbreaks is targeting the development and implementation of early warning systems, which indicate qualitatively and quantitatively the presence of a pathogen. As toxin contaminated food and drink are a potential threat to human health and consequently have a significant socioeconomic impact worldwide, the detection of pathogenic bacteria remains not only a big scientific challenge but also a practical problem of enormous significance. Numerous analytical methods, including conventional culturing and staining techniques as well as molecular methods based on polymerase chain reaction amplification and immunological assays, have emerged over the years and are used to identify and quantify pathogenic agents. While being highly sensitive in most cases, these approaches are highly time, labor, and cost consuming, requiring trained personnel to perform the frequently complex assays. A great challenge in this field is therefore to develop rapid, sensitive, specific, and if possible miniaturized devices to validate the presence of pathogens in cost and time efficient manners. Electrochemical sensors are well accepted powerful tools for the detection of disease-related biomarkers and environmental and organic hazards. They have also found widespread interest in the last years for the detection of waterborne and foodborne pathogens due to their label free character and high sensitivity. This Review is focused on the current electrochemical-based microorganism recognition approaches and putting them into context of other sensing devices for pathogens such as culturing the microorganism on agar plates and the polymer chain reaction (PCR) method, able to identify the DNA of the microorganism. Recent breakthroughs will be highlighted, including the utilization of microfluidic devices and immunomagnetic separation for multiple pathogen analysis in a single device. We will conclude with some perspectives and outlooks to better understand shortcomings. Indeed, there is currently no adequate solution that allows the selective and sensitive binding to a specific microorganism, that is fast in detection and screening, cheap to implement, and able to be conceptualized for a wide range of biologically relevant targets.

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Ultrathin carbon nanoparticle -poly(diallyldimethylammonium chloride) films (CNP-PDDAC films) are formed on tin-doped indium oxide (ITO) electrodes in a layer-by-layer electrostatic deposition process employing 9 -18 nm diameter carbon particles. Transparent and strongly adhering films of high electrical conductivity are formed and characterized in terms of their electrochemical reactivity. When immersed in aqueous 0.1 M phosphate buffer pH 7, each layer of CNP-PDDAC (of ca. 5 -6 nm average thickness) is adding an interfacial capacitance of ca. 10 mF cm À2. Absorption into the CNP -PDDAC nanocomposite film is dominated by the sites in the PDDAC cationomer and therefore anionic molecules such as indigo carmine are strongly bound and retained within the film (cationic binding sites per layer ca. 150 pmol cm À2 ). In contrast, cationic redox systems such as ferrocenylmethyltrimethyl-ammonium þ fail to bind. For solution phase redox systems such as hydroquinone, the rate of electron transfer is dramatically affected by the CNP-PDDAC film and switched from completely irreversible to highly reversible even with a single layer of carbon nanoparticles. For the mixed redox system ascorbate -dopamine in 0.1 M phosphate buffer pH 7 cyclic voltammograms suggest a rapid and selective temporary poisoning process which causes the ascorbate oxidation to be suppressed in the second potential cycle. This effect is exploited for the detection of micromolar concentrations of dopamine in the presence of millimolar ascorbate.

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Co3O4/CoFe2O4 decorated on nickel foam (NF/Co3O4/CoFe2O4) was synthesized from a metal–organic framework by a solvothermal approach using nicotinic acid as an organic linker followed by annealing at 500 °C. The electrochemical activity of NF/Co3O4/CoFe2O4 for the oxygen evolution reaction (OER) was assessed in alkaline medium. Under basic conditions (pH > 10), the composite electrode revealed enhanced electrocatalytic OER activity requiring an overpotential of 215 mV versus RHE to reach 10 mA cm–2 with a Tafel slope of 90 mV dec–1. The enhanced OER activity was ascribed to the presence of Co3+ and Fe3+ in the octahedral sites of Co3O4 and CoFe2O4, respectively, and their synergic effect in Co3O4/CoFe2O4. This anode showed a stable current density of about 160 mA cm–2 for 20 h; the same Co3O4/CoFe2O4/NF anode was applied for several OER experiments without loss of activity.

In this research, graphitic carbon nitride (g-C 3 N 4 ) was synthesized using pyrolysis of melamine and its phase, morphology, composition, and structure were characterized by using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, energy dispersive analysis of X-rays, and FT-IR spectroscopy. The modification of carbon paste electrode with g-C 3 N 4 /chitosan composite has been performed using the casting method. Experimental results demonstrated the superb adsorptive properties of g-C 3 N 4 /chitosan composite through Hg(II). Differential pulse voltammetry (DPV) was applied for quantitative determinations. The linear calibration curves is obtained in the ranges of 1.0 × 10 −6 to 8.0 × 10 −5 mol L −1 and 1.0 × 10 −7 to 5.0 × 10 −6 mol L −1 . The proposed protocol can offer a highly selective and sensitive method for the detection of Hg(II) with a detection limit of 1.0 × 10 −8 mol L −1 . Determination of Hg(II) was performed in the presence of Fe(II) and Cu(II). Finally, the modified electrode has been applied for sensitive determination of Hg(II) in real samples.