In this paper, the relative humidity sensor properties of graphene oxide (GO) and graphene oxide/multiwalled nanotubes (GO/MWNTs) composites have been investigated. Composite sensors were fabricated by direct laser scribing and characterized using UV-vis-NIR, Raman, Fourier transform infrared, and X-ray photoemission spectroscopies, electron scanning microscopy coupled with energy-dispersive X-ray analysis, and impedance spectroscopy (IS). These methods confirm the composite homogeneity and laser reduction of GO/MWNT with dominant GO characteristics, while ISresults analysis reveals the circuit model for rGO-GO-rGO structure and the effect of MWNT on the sensor properties. Although direct laser scribing of GO-based humidity sensor shows an outstanding response (|ΔZ|/|Z| up to 638,800%), a lack of stability and repeatability has been observed. GO/MWNT-based humidity sensors are more conductive than GO sensors and relatively less sensitive (|ΔZ|/|Z| = 163,000%). However, they are more stable in harsh humid conditions, repeatable, and reproducible even after several years of shelf-life. In addition, they have fast response/recovery times of 10.7 s and 9.3 s and an ultra-fast response time of 61 ms when abrupt humidification/dehumidification is applied by respiration. All carbon-based sensors’ overall properties confirm the advantage of introducing the GO/MWNT hybrid and laser direct writing to produce stable structures and sensors.

An electrochemical sensor for the pesticide Pirimicarb (PMC) has been developed. A screen-printed electrode (SPCE) was used and modified with the conducting polymer poly (3,4-ethylenedioxythiophene) (PEDOT) and gold nanoparticles (AuNPs) to enhance electrochemical proprieties. Electrode characterizations were performed using scattering electron microscopy (SEM) and cyclic voltammetry (CV). With the SPCE/PEDOT:PSS/AuNPs modified electrode, a new peak at 1.0 V appeared in the presence of PMC related to the PMC oxidation. To elucidate the mechanism of PMC oxidation, Gas Chromatography-Mass Spectrometry (GC-MS), where two major peaks were identified, evidencing that the device can both detect and degrade PMC by an electro-oxidation process. Exploring this peak signal, it was possible the sensor development, performing detection from 93.81–750 µmol L⁻¹, limits of quantification (LOQ) and detection (LOD) of 93.91 µmol L⁻¹ and 28.34 µmol L⁻¹, respectively. Thus, it was possible to study and optimization of PMC degradation, moreover, to perform detection at low concentrations and with good selectivity against different interferents using a low-cost printed electrode based on graphite modified with conductive polymer and AuNPs.

Malathion (MLT), a widely used organophosphate pesticide for global pest control, presents substantial risks to both human health and ecosystems. Therefore, the development of a rapid and efficient detection method is critical to mitigate its harmful effects. This study proposes a novel thin-film impedimetric sensor designed for the reliable detection of MLT pesticide residues based on laser-induced graphene electrodes coated with a sensing composite material comprising graphene oxide, 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF₆), and silver nanoparticles. Mechanical and electrochemical stability is enhanced by the integration of polyvinyl chloride and 2-nitrophenyl octyl ether into framework materials. The sensor exhibited excellent sensitivity towards MLT in the concentration range of 1 nM to 200 nM. The charge transfer resistance R_ct increases by 304.08% at a concentration of 200 nM. The sensor shows minimal interference and good reproducibility and repeatability. A change in R_ct of 15.61% over 30 days confirms good stability. Using framework materials enhances the long-term stability by 11.45 times compared to sensors without them. The synergistic effects of the three sensitive materials and the structural support from polyvinyl chloride (PVC) and 2-Nitrophenyl octyl ether (o-NPOE) enable outstanding detection capabilities. The novel sensor has a high potential for pesticide residue detection in the environment providing a reliable and efficient tool for preserving ecosystems, supporting sustainable agriculture, and ensuring compliance with environmental regulations.

One of the lessons we learned from the COVID-19 pandemic is that the need for ultrasensitive detection systems is now more critical than ever. While sensors’ sensitivity, portability, selectivity, and low cost are crucial, new ways to couple synergistic methods enable the highest performance levels. This review article critically discusses the synergetic combinations of optical and electrochemical methods. We also discuss three key application fields—energy, biomedicine, and environment. Finally, we selected the most promising approaches and examples, the open challenges in sensing, and ways to overcome them. We expect this work to set a clear reference for developing and understanding strategies, pros and cons of different combinations of electrochemical and optical sensors integrated into a single device.