A paper-based solid-phase assay is presented for transduction of nucleic acid hybridization using immobilized quantum dots (QDs) as donors in fluorescence resonance energy transfer (FRET). The surface of paper was modified with imidazole groups to immobilize QD-probe oligonucleotide conjugates that were assembled in solution. Green-emitting QDs (gQDs) were FRET-paired with Cy3 acceptor. Hybridization of Cy3-labeled oligonucleotide targets provided the proximity required for FRET-sensitized emission from Cy3, which served as an analytical signal. The assay exhibited rapid transduction of nucleic acid hybridization within minutes. Without any amplification steps, the limit of detection of the assay was found to be 300 fmol with the upper limit of the dynamic range at 5 pmol. The implementation of glutathione-coated QDs for the development of nucleic acid hybridization assay integrated on a paper-based platform exhibited excellent resistance to nonspecific adsorption of oligonucleotides and showed no reduction in the performance of the assay in the presence of large quantities of noncomplementary DNA. The selectivity of nucleic acid hybridization was demonstrated by single-nucleotide polymorphism (SNP) detection at a contrast ratio of 19 to 1. The reuse of paper over multiple cycles of hybridization and dehybridization was possible, with less than 20% reduction in the performance of the assay in five cycles. This work provides an important framework for the development of paper-based solid-phase QD-FRET nucleic acid hybridization assays that make use of a ratiometric approach for detection and analysis.

As teaching laboratories stand empty in light of COVID-19, we extended the practical experience from the laboratory to the safety of the students’ homes. We developed a simple, robust, and versatile at-home experiment that teaches solution preparation, calibration curves, real-life sample preparation, and data analysis to second-year analytical chemistry students. Solutions were prepared using common kitchen tools and readily available corn starch, syringes, and trophic iodine for a low cost below $20. A calibration curve for the brightness of corn starch–iodine solutions as a function of starch concentration was prepared. Solutions were imaged using a smartphone camera, and the brightness of each solution was quantified using ImageJ. Starch was extracted from a ripe banana and quantified using the calibration curve. Extending the practical experience to students’ homes in the age of COVID-19 not only provides them with a better sense of the real chemistry laboratory they will one day return to but also helps solidify and expand on key concepts learned in the virtual classroom.

Quantum dots (QDs) have been widely used in chemical and biosensing due to their unique photoelectrical properties and are well suited as donors in fluorescence resonance energy transfer (FRET). Selective hybridization interactions of oligonucleotides on QDs have been determined by FRET. Typically, the QD-FRET constructs have made use of labeled targets or have implemented labeled sandwich format assays to introduce dyes in proximity to the QDs for the FRET process. The intention of this new work is to explore a method to incorporate the acceptor dye into the probe molecule. Thiazole orange (TO) derivatives are fluorescent intercalating dyes that have been used for detection of double-stranded nucleic acids. One such dye system has been reported in which single-stranded oligonucleotide probes were doubly labeled with adjacent thiazole orange derivatives. In the absence of the fully complementary (FC) oligonucleotide target, the dyes form an H-aggregate, which results in quenching of fluorescence emission due to excitonic interactions between the dyes. The hybridization of the FC target to the probe provides for dissociation of the aggregate as the dyes intercalate into the double stranded duplex, resulting in increased fluorescence. This work reports investigation of the dependence of the ratiometric signal on the type of linkage used to conjugate the dyes to the probe, the location of the dye along the length of the probe, and the distance between adjacent dye molecules. The limit of detection for 34mer and 90mer targets was found to be identical and was 10 nM (2 pmol), similar to analogous QD-FRET using labeled oligonucleotide target. The detection system could discriminate a one base pair mismatch (1BPM) target and was functional without substantial compromise of the signal in 75% serum. The 1BPM was found to reduce background signal, indicating that the structure of the mismatch affected the environment of the intercalating dyes.

Advancements in technology have led to significant changes in the workforce and created a demand for expertise in science, technology, engineering, and mathematics (STEM). In response, curricula have evolved to emphasize essential skills such as critical thinking and communication to prepare students for STEM-based careers. To this end, postsecondary institutions continue to develop and incorporate project-based learning (PBL), course-based undergraduate research experiences (CUREs), and process-oriented guided-inquiry learning (POGIL). These opportunities can be offered in junior level (1st and 2nd year) courses by designing projects that match students' skills and knowledge. Opportunities at the junior level reach a larger student population and can increase interest in STEM-based careers. In this article, we introduce a project-based activity for the second-year analytical chemistry laboratory in which students design and conduct experiments to quantify analytes in real-life samples. Analytes selected for this project (acids or bases, ascorbic acid, betacarotene, calcium, oxalate, reducing sugars and starch) can be quantified using techniques familiar to second year students including titration and absorbance spectroscopy. Students first designed experimental procedures and received feedback before conducting the experiments. Each experiment was performed over two laboratory periods, which allowed students to modify procedures between iterations to improve their experimental design. This experience allowed students to develop 21st century competencies including critical thinking and problem solving, innovation, creativity and entrepreneurship, self-directed learning, collaboration, and communication.

Paper-based platform for the selective detection of DNA targets by hybridization using FRET between intrinsically labeled fluorescent DNA probes and quantum dots.