DNA-functionalized gold nanoparticles have been increasingly applied as sensitive and selective analytical probes and biosensors. The DNA ligands bound to a nanoparticle dictate its reactivity, making it essential to know the type and number of DNA strands bound to the nanoparticle surface. Existing methods used to determine the number of DNA strands per gold nanoparticle (AuNP) require that the sequences be fluorophore-labeled, which may affect the DNA surface coverage and reactivity of the nanoparticle and/or require specialized equipment and other fluorophore-containing reagents. We report a UV-visible-based method to conveniently and inexpensively determine the number of DNA strands attached to AuNPs of different core sizes. When this method is used in tandem with a fluorescence dye assay, it is possible to determine the ratio of two unlabeled sequences of different lengths bound to AuNPs. Two sizes of citrate-stabilized AuNPs (5 and 12 nm) were functionalized with mixtures of short (5 base) and long (32 base) disulfide-terminated DNA sequences, and the ratios of sequences bound to the AuNPs were determined using the new method. The long DNA sequence was present as a lower proportion of the ligand shell than in the ligand exchange mixture, suggesting it had a lower propensity to bind the AuNPs than the short DNA sequence. The ratio of DNA sequences bound to the AuNPs was not the same for the large and small AuNPs, which suggests that the radius of curvature had a significant influence on the assembly of DNA strands onto the AuNPs.

During the Spring 2020 semester, many institutions abruptly transitioned their courses from face-to-face instruction to remote learning in response to the COVID-19 pandemic. To address the unique challenges posed by the remote teaching and learning modality, our department used mobile technology to adapt empirically validated instructional strategies for use in our remote courses. At Merrimack College, all faculty and students have iPads and Apple Pencils, and the members of the Department of Chemistry and Biochemistry have incorporated this mobile technology into all of our course offerings. Our continued use of this technology eased the transition for both faculty and students by promoting course continuity and decreasing the cognitive load imposed by the transition. Survey responses suggest that students appreciated the structure provided by scaffolded course materials and synchronous class meetings, which helped keep them engaged in their chemistry courses. Coupling active learning instruction with the Zoom video conferencing platform allowed students to connect with the instructor and other students; this was highly valued by our students. Overall, we can conclude that universal access to technology, creating community using videoconferencing software, and intentional pedagogical choices to incorporate active learning created a positive learning environment for students.

Systematic determination of the relationship between nanoparticle core diameter and toxicity for a series of structurally analogous gold nanoparticles in zebrafish

General chemistry students need to understand the concept of intermolecular forces and use them to predict the properties of materials. To do this, they must create symbolic representations of molecules, relate these to physical observations, and explain them using submicroscopic theoretical constructs. When these concepts are taught separately, students lack the context to fully understand and retain them. In this inquiry-based laboratory experiment, students explored the interrelated concepts of molecular structure and solubility in an applied context and then explained their individual results and the class results using the concept of intermolecular forces. Specifically, they drew the molecular structures of an analogous series of alcohol molecules and evaluated the relative solubility of the alcohols in polar versus nonpolar solvents. Designing the procedure to avoid student exposure to hazardous reagents facilitated their exploration of the underlying concepts. Using Sharpie pigment in each alcohol as an indicator dye helped the students visually assess their relative solubility in different solvents. Students typically observed that the relative solubility of the alcohols in the solvents could be predicted based on key factors that affect molecular polarity and hydrophobicity, in particular hydrocarbon chain length and surface-to-volume ratios. The students explained the pooled class solubility results based on the types and strengths of intermolecular forces present in each substance. Significance testing performed on our pre-and postlaboratory quiz data indicate that completing this experiment significantly improved students' conceptual understanding of structure−property relationships. Item difficulty and discrimination index scores were used to validate these quiz questions.