The relative stability of Sc, Ti, and V encapsulating Ge(n) clusters in the size range n = 14-20 has been studied through first-principles electronic structure calculations based on density functional theory. Variations of the embedding energy, gap between the highest occupied and the lowest occupied molecular orbitals, ionization potential, vertical detachment energy, and electron affinity with cluster size have been calculated to identify clusters with enhanced stability. The enhanced stability of some clusters can be very well explained as due to the formation of a filled shell free-electron gas inside the Ge cages. For the first time, direct evidence of the formation of a free-electron gas is also presented. In some other clusters, enhanced stability is found to originate from geometric effects. Some clusters that may be expected to have enhanced stability from simple electron counting rules do not show that. These results provide new insights into the long-standing question of whether electron counting rules can explain the relative stability of transition metal encapsulated semiconductor clusters and show that these clusters are too complex for such simple generalizations.

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Abstract2D graphene oxide (GO) with large surface area, multivalent structure can easily bind single-stranded DNA/RNA (aptamers) through hydrophobic/π-stacking interactions, whereas aptamers having small size, excellent chemical stability and low immunogenicity bind to their targets with high affinity and specificity. GO–aptamer conjugate materials synthesized by integrating aptamers with GO can thus provide a better alternative to antibody-based strategies for cancer diagnostic and therapy. Moreover, GO’s excellent fluorescence quenching properties can be utilized to develop efficient fluorescence-sensing platforms. In this review, recent advances in GO–aptamer conjugate materials for the detection of major cancer biomarkers have been discussed.