In the present work, a novel, portable and innovative eNose composed of a surface acoustic wave (SAW) sensor array based on zeolitic imidazolate frameworks, ZIF-8 and ZIF-67 nanocrystals (pure and combined with gold nanoparticles), as sensitive layers has been tested as a non-invasive system to detect different disease markers, such as acetone, ethanol and ammonia, related to the diagnosis and control of diabetes mellitus through exhaled breath. The sensors have been prepared by spin coating, achieving continuous sensitive layers at the surface of the SAW device. Low concentrations (5 ppm, 10 ppm and 25 ppm) of the marker analytes were measured, obtaining high sensitivities, good reproducibility, short time response and fast signal recovery.

The aim of this work was to study the effect of oxidative stress on the structural changes of the secondary peptide structure of amyloid beta 1–42 (Aβ 1–42), in the dentate gyrus of hippocampus of rats exposed to low doses of ozone. The animals were exposed to ozone-free air (control group) and 0.25 ppm ozone during 7, 15, 30, 60, and 90 days, respectively. The samples were studied by: 1) Raman spectroscopy to detect the global conformational changes in peptides with α-helix and β-sheet secondary structure, following the deconvolution profile of the amide I band; and 2) immunohistochemistry against Aβ 1–42. The results of the deconvolutions of the amide I band indicate that, ozone exposure causes a progressively decrease in the abundance percentage of α-helix secondary structure. Furthermore, the β-sheet secondary structure increases its abundance percentage. After 60 days of ozone exposure, the β-sheet band is identified in a similar wavenumber of the Aβ 1–42 peptide standard. Immunohistochemistry assays show an increase of Aβ 1–42 immunoreactivity, coinciding with the conformational changes observed in the Raman spectroscopy of Aβ 1–42 at 60 and 90 days. In conclusion, oxidative stress produces changes in the folding process of amyloid beta peptide structure in the dentate gyrus, leading to its conformational change in a final β-sheet structure. This is associated to an increase in Aβ 1–42 expression, similar to the one that happens in the brain of Alzheimer’s Disease patients.

Chronic inflammatory diseases, such as cancer, diabetes mellitus, stroke, ischemic heart diseases, neurodegenerative conditions, and COVID-19 have had a high number of deaths worldwide in recent years. The accurate detection of the biomarkers for chronic inflammatory diseases can significantly improve diagnosis, as well as therapy and clinical care in patients. Graphene derivative materials (GDMs), such as pristine graphene (G), graphene oxide (GO), and reduced graphene oxide (rGO), have shown tremendous benefits for biosensing and in the development of novel biosensor devices. GDMs exhibit excellent chemical, electrical and mechanical properties, good biocompatibility, and the facility of surface modification for biomolecular recognition, opening new opportunities for simple, accurate, and sensitive detection of biomarkers. This review shows the recent advances, properties, and potentialities of GDMs for developing robust biosensors. We show the main electrochemical and optical-sensing methods based on GDMs, as well as their design and manufacture in order to integrate them into robust, wearable, remote, and smart biosensors devices. We also describe the current application of such methods and technologies for the biosensing of chronic disease biomarkers. We also describe the current application of such methods and technologies for the biosensing of chronic disease biomarkers with improved sensitivity, reaching limits of detection from the nano to atto range concentration.

Dopamine (DA) regulates several functions in the central nervous system and its depletion is responsible for psychological disorders like Parkinson's disease. Several analytical approaches have been presented for DA detection in pathological diagnosis. SERS spectroscopy is a highly promising technique for the sensitive detection of DA. However, an improvement in its detection in aqueous solution is highly desirable for reliable quantification in biological fluids. In this work, we explored a label-free SERS approach for DA detection, employing two conventional methods to synthesize Ag colloids: reduction via citrates (c-AgNPs) and reduction via hydroxylamine (h-AgNPs), and SERS measurements were performed with a laser at 488 nm wavelength. Under these conditions, DA was identified through reproducible SERS spectra in the c-AgNP medium; however, the SERS spectra of DA in h-AgNP solution showed a completely different SERS profile. SERS band analysis revealed that DA in h-AgNPs was oxidized and converted into polydopamine (PDA), which was triggered after exposure to laser radiation. DA oxidation and PDA formation were followed over time through the SERS band profile at pH 7, 9 and 12. We found that in situ PDA formation started after 50 min of laser irradiation of DA at pH 7, while DA was quickly oxidized at pH 9 and 12. Here, we present a detailed SERS band analysis of PDA, which sheds light on the molecular steps in the pathway formation of the PDA structure. Spectroscopic analysis and characterization revealed that a long laser exposure time led to the formation of stable PDA complexes with AgNPs, which allowed us to propose a novel approach for synthesis of AgNP–PDA composites. In conclusion, to detect DA through a label-free SERS approach, c-AgNPs must be employed, while stable AgNP–PDA materials can be achieved with h-AgNPs and 488 nm laser excitation.

Recombinant human interleukin-6 (IL-6) is a key cytokine that plays an important role in the immune system and inflammatory response, explaining why any modification of its concentration in biological fluids is considered a signal of a pathological condition. Therefore, it is important to develop alternative, highly sensitive and reliable analytical methodologies to detect and identify this analyte in biological fluids. Herein, we present a proof of concept for the development of a new analytical hybrid platform for IL-6 detection that is based on the combination of drop-coating deposition Raman (DCDR) spectroscopy and graphene-enhanced Raman spectroscopy (GERS) effects. The sensitivity limits for IL-6 detection were found to be a function of the type of substrate used. When a 1 μL droplet of IL-6 solution is deposited and dried on an Si substrate, a DCDR effect occurs, and a detection limit below 1 ng mL⁻¹ is obtained; however, when the same is performed using a hybrid substrate of reduced graphene oxide and silicon (rGO/Si), the joint action of DCDR and GERS effects results in a detection limit well below 1 pg mL⁻¹. It is important to note that this result implies the absolute mass detection of 1 fg of IL-6. In summary, the Raman spectroscopy DCDR/GERS analytical platform proposed here allows the reliable identification of, as well as the very sensitive detection of, IL-6 and promises to improve the performance of clinical evaluations of this biomarker that are currently in use. In this study, the Raman spectra of IL-6 in powder and solution, together with the corresponding band assignment, are presented for the first time in the literature.