João Luis Machado Santos

The development of more accessible perfumes (non-counterfeit replicas) that offer a similar scent to luxury perfume brands is an emerging trend in the perfume market. In this context, it is important to develop simple, rapid, cost-effective, and environmentally friendly alternative analytical tools capable of differentiating original perfumes from their non-counterfeit replicas. In this work, three vibrational spectroscopic techniques, namely near-infrared (NIR), mid-infrared (MIR), and Raman spectroscopy, were evaluated for the discrimination between original perfume samples and their non-counterfeit replicas. Several original perfume samples and their non-counterfeit replicas were scanned through these vibrational spectroscopic techniques and analyzed with two chemometric tools: principal component analysis (PCA) and hierarchical cluster analysis (HCA). Different pre-processing techniques were also tested in PCA and HCA to attest to the robustness of the findings. The results revealed that all vibrational spectroscopic techniques tested demonstrated high efficiency in differentiating original perfumes from their non-counterfeit replicas. NIR spectroscopy revealed the least similarity among the samples across all pre-processing techniques. In this context, these vibrational spectroscopic techniques are a rapid, cost-effective, non-destructive, and interesting alternative for discriminating between original perfume samples and non-counterfeit replicas. Although further studies, including the application of supervised classification methods to a larger sample set, are needed to attest to the robustness of these results, these preliminary results are very interesting and promising. To the best of our knowledge, this was the first time that vibrational spectroscopic techniques were applied and compared in the analysis of perfume and non-counterfeit replicas.

Dual-emission photoluminescence (PL) nanoprobes provide improved analytical performance to develop a reliable and sensitive sensing platform for quantifying chloramphenicol in pharmaceutical samples, thereby ensuring therapeutic efficacy and patient safety. In this work, a dual-emission PL sensing platform combining carbon dots (CDs) and AgInS₂ quantum dots (QDs) capped with mercaptopropionic acid (MPA) was developed for the quantitative determination of chloramphenicol, resorting to chemometric methods for data analysis. CDs, CdTe QDs, and AgInS₂ QDs were synthesized and individually evaluated considering their photostability, PL response and kinetics of their interaction with the antibiotic. After this, two dual-emission probes, CDs/MPA-CdTe and CDs/MPA-AgInS₂, were prepared and assessed based on the complementarity of their individual emission features. The obtained kinetic PL dataset was processed using unfolded partial least squares (U-PLS) in order to explore the multidimensional information of the dual-emission systems and to evaluate the performance of both sensing platforms. CDs/MPA-AgInS₂ probe was demonstrated to be the most efficient sensing platform due to its better compromise between sensitivity and photostability, as well as its cadmium-free composition, allowing the implementation of a more environmentally friendly analytical methodology. The optimization of the U-PLS models involved the assessment of the kinetic acquisition time and different spectral regions. The results showed that reliable, sensitive and efficient quantification could be achieved within the first 5 min of interaction and using the full emission spectrum of the sensing probe. Additionally, different interaction mechanisms were observed for each nanomaterial in the combined probe, being static for the CDs/chloramphenicol interaction and dynamic for MPA-AgInS₂/chloramphenicol interaction, which supports the synergetic behavior of the combined probe. The proposed methodology was effectively applied to commercial pharmaceutical formulations, yielding accurate results with good figures of merit. Therefore, this approach can be used as a relevant alternative to existing methodologies for a rapid, robust, and environmentally friendly method for chloramphenicol quantification.

Dual-emission molecularly imprinted membranes (dual@MIPs@mbr) were developed as a proof-of-concept platform for the selective and instrument-free detection of the cancer biomarker carbohydrate antigen 19-9 (CA 19-9). The system integrates a ratiometric fluorescence response by embedding yellow-emitting quantum dots (y-QDs), serving as target-responsive probes, and blue-emitting carbon dots (b-CDs), acting as an internal reference, within a CA 19-9-imprinted polymeric matrix. Specific rebinding of CA 19-9 to the imprinted cavities induced selective quenching of the y-QDs while preserving the b-CDs emission, yielding a visible color shift from yellow/green to blue. This behavior enabled the quantification of CA 19-9 over a linear range of 4–400 U mL⁻¹, with a limit of detection of 0.056 U mL⁻¹ in diluted serum. The membranes showed good selectivity against common serum interferents and maintained short-term photochemical stability. Although the method has not yet been validated using real clinical samples, the pronounced ratiometric response and simple visual readout demonstrate its potential as a low-cost, portable sensing approach for future point-of-care cancer biomarker analysis.

Background/Objectives: Carbohydrate antigen 19-9 (CA19-9) is a clinically established biomarker primarily used for monitoring disease progression and recurrence in pancreatic and gastrointestinal cancers. Accurate and continuous quantification of CA19-9 in patient samples is critical for effective clinical management. This study aimed to develop dual-emitting molecularly imprinted nanopolymers (dual@nanoMIPs) for ratiometric and reliable detection of CA19-9 in serum. Methods: Dual-emitting nanoMIPs were synthesized via a one-step molecular imprinting process, incorporating both blue-emitting carbon dots (b-CDs) as internal reference fluorophores and yellow-emitting quantum dots (y-QDs) as responsive probes. The CA19-9 template was embedded into the polymer matrix to create specific recognition sites. Fluorescence measurements were carried out under 365 nm excitation in 1% human serum diluted in phosphate-buffered saline (PBS). Results: The dual@nanoMIPs exhibited a ratiometric fluorescence response upon CA19-9 binding, characterized by the emission quenching of the y-QDs at 575 nm, while the b-CDs emission remained stable at 467 nm. The fluorescence shift observed in the RGB coordinates from yellow to green in the concentration range of CA19-9 tested, improved quantification accuracy by compensating for matrix effects in serum. A linear detection range was achieved from 4.98 × 10⁻³ to 8.39 × 10² U mL⁻¹ in serum samples, with high specificity and reproducibility. Conclusions: The dual@nanoMIPs developed in this work enable a stable, sensitive, and specific detection of CA19-9 in minimally processed serum, offering a promising tool for longitudinal monitoring of cancer patients. Its ratiometric fluorescence design enhances reliability, supporting clinical decision-making in the follow-up of pancreatic cancer.

The acquisition of kinetic data in QD-based PL sensing methodologies has been revealed to be an auspicious alternative in applying these nanomaterials in analytical chemistry, enabling enhanced discrimination and quantification of analytes, even in complex sample matrices. The accessibility of kinetic measurements, which use routine laboratory instrumentation, is a significant advantage that increases the practicality of this methodology. The simple acquisition of these kinds of second-order data combined with chemometric analysis can ensure accurate results in environmental, biomedical, and food monitoring applications. These developments emphasize the vital importance of kinetic approaches in increasing sensitivity, improving analyte discrimination, and making the application of QDs in complex samples possible.

Accurate and selective monitoring of thiamine levels in multivitamin supplements is essential for preventing deficiencies and ensuring product quality. To achieve this, a Förster resonance energy transfer (FRET) system using carbon dots (CDs) as energy donors and citrate-stabilized silver nanoparticles (AgNPs) as energy acceptors was developed. The aqueous synthesis of AgNPs using microwave irradiation was optimized to obtain efficient plasmonic nanoparticles for FRET applications, targeting maximal absorbance intensity, stability, and wavelength alignment. Using a central composite orthogonal design (CCOD), the optimal conditions were identified as a 12.5 min microwave reaction time, a Ag molar ratio of 0.72, and a pH of 8.28. The FRET sensing scheme was applied for thiamine determination, where the vitamin’s presence impaired the FRET process, restoring CDs’ photoluminescence (PL) emission in a concentration-dependent manner. To mitigate interference from other vitamins, PL kinetic data and excitation–emission matrix (EEM) data were analyzed using unfolded partial least-squares (U-PLS) with the subsequent application of the residual bilinearization technique (RBL), achieving high sensitivity and specificity for thiamine detection. This method demonstrated its accuracy and robustness by attaining a determination coefficient (R²) of 0.952 and a relative error of prediction (REP%) of 11%. This novel method offers highly sensitive and interference-free thiamine detection, with significant potential for a wide range of analytical applications.

Metal ion pollution poses a global concern due to its significant risks to both human health and environmental well-being. The toxicity of these ions can increase when they coexist, interacting with each other and with other harmful substances, even at low concentrations. Therefore, an accurate, rapid, and cost-effective methodology is urgently needed for the simultaneous quantification of multiple metal ions. This study presents a new approach for the multiplexed detection of various metal ions (Ag⁺, Cu²⁺, Hg²⁺, Al³⁺, Pb²⁺, Fe³⁺, Fe²⁺, Zn²⁺, Ni²⁺, Cd²⁺, and Ca²⁺) using a triple-emission nanoprobe comprising carbon dots and distinctly capped CdTe quantum dots, specifically green-emitting glutathione -quantum dots and red-emitting 3-mercaptopropionic acid-quantum dots. The method achieved high accuracy by analysing first- and second-order photoluminescence data with distinct advanced chemometric tools. R²_P values for partial least squares and unfolded partial least square models exceeding 0.9 for several metal ions at low concentrations (mmol L⁻¹) were obtained. Additionally, PL second-order data yielded significantly better results than PL first-order data, attributed to the distinct behaviour of the metal ions over time. Interestingly, it was also noted for the first time the significant contribution of the molar ratio between the metal ions on the models’ accuracy. This novel method provides a highly accurate and efficient way to detect multiple metal ions simultaneously, paving the way for improved environmental monitoring and pollution assessment. The utilization of the proposed method contributes to a better understanding of the complex interactions in mixed metal ion systems, allowing for earlier detection and mitigation of metal ion contamination threats. Graphical Abstract