Semiconductor quantum dots (QDs) exhibit unique optical and photophysical properties that offer significant advantages over organic dyes as optical labels for chemo/bio-sensing. This review addresses the methods for metal ion detection with QDs, including photoluminescent, electrochemiluminescent, photoelectrochemical, and electrochemical approaches. The main mechanisms of direct interaction between QDs and metal ions which lead to photoluminescence being either off or on, are discussed in detail. These direct interactions provide great opportunities for developing simple yet effect metal ion probes. Different methods to design the chemically-modified QD hybrid structures through anchoring metal ion-specific groups onto the surface of QDs are summarized. Due to the spatial separation of the luminescence center and analyte recognition sites, these chemically-modified QDs offer greatly improved sensitivity and selectivity for metal ions. Several interesting applications of QD-based metal ion probes are presented, with specific emphasis on cellular probes, coding probes and sensing with logic gate operations.
Divergent interpretations have appeared in the literature regarding the structural nature and evolutionary behavior for photoluminescent CdSe nanospecies with sharp doublets in optical absorption. We report a comprehensive description of the transformation pathway from one CdSe nanospecies displaying an absorption doublet at 373/393 nm to another species with a doublet at 433/460 nm. These two nanospecies are zero‐dimensional (0D) magic‐size clusters (MSCs) with 3D quantum confinement, and are labeled dMSC‐393 and dMSC‐460, respectively. Synchrotron‐based small‐angle X‐ray scattering (SAXS) returns a radius of gyration of 0.92 nm for dMSC‐393 and 1.14 nm for dMSC‐460, and indicates that both types are disc shaped with the exponent of the SAXS form factor equal to 2.1. The MSCs develop from their unique counterpart precursor compounds (PCs), which are labeled PC‐393 and PC‐460, respectively. For the dMSC‐393 to dMSC‐460 transformation, the proposed PC‐enabled pathway is comprised of three key steps, dMSC‐393 to PC‐393 (Step 1), PC‐393 to PC‐460 (Step 2 involving monomer addition), and PC‐460 to dMSC‐460 (Step 3). The present study provides a framework for understanding the PC‐based evolution of MSCs and how PCs enable transformations between MSCs.
An
approach is reported for the exclusive production of CdTe magic-size
clusters (MSCs) that exhibit an optical absorption doublet peaking
at 385/427 nm, with an explanation of the synthesis procedure. The
MSCs, defined as dMSC-427, were produced from the reaction of cadmium
oleate (Cd(OA)2) and tri-n-octylphosphine
telluride in octadecene at 100 °C, with the addition of acetic
acid (HOAc) or acetate (M(OAc)2) during the prenucleation
stage (40 °C). Without such an addition or when it was performed
in the postnucleation stage (100 °C), quantum dots (QDs) developed.
The production of dMSC-427 or QDs is hypothesized to be related to
the solubility of the Cd precursor, such as Cd(OA)1(OAc)1 or Cd(OA)2, respectively. Also, the reactions
that lead to Cd(OA)1(OAc)1 are proposed. The
present study provides an in-depth understanding of the two-pathway
model proposed for the prenucleation stage of binary colloidal QDs,
as well as of the formation of MSCs and/or QDs.
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