Dispersible Plasmonic Doped Metal Oxide Nanocrystal Sensors that Optically Track Redox Reactions in Aqueous Media with Single‐Electron Sensitivity

Abstract

chemical, biochemical, and even biological species ( Figure 1 ). Furthermore, their distinctive near-infrared (NIR) optical response can be quantitatively interpreted [ 14,15 ] so that these redox processes can be tracked with single-electron sensitivity. To demonstrate their exciting new properties in interrogating complex redox systems, we use them to quantify chemically driven charge transfer across the electrifi ed cell membranes of Shewanella oneidensis MR-1, requiring only a simple optical readout and absent any external electrodes. Results and DiscussionRecently, it was shown that the characteristic wavelength and intensity of the NIR plasmon resonance absorption of tin-doped indium oxide (ITO) nanocrystals bound to an electrode can be strongly modulated in a reversible manner using a directional voltage bias. [ 9,16 ] These changes arise from the dependence of the Electron transfer in complex aqueous systems can be observed remotely with single-electron sensitivity using locally dispersed nanostructures conferred with electronic charge concentration-dependent plasmonic properties. When introduced to a system out of redox equilibrium, tin-doped indium oxide nanocrystals undergo rapid multielectron transfer until redox equilibrium is reached; this modulates their free carrier concentration and plasmonic optical properties in the spectrally isolated near-infrared. This capability is harnessed here to noninvasively track, model, and quantify electron transfer events reversibly for organic, inorganic, biogenic, and even living cells.Adv. Optical Mater. 2015, 3, 1293-1300 www.MaterialsViews.com www.advopticalmat.de Figure 1. Plasmonic doped metal oxide nanocrystals reversibly exchange electrons with redox-active small molecules, biomacromolecules, and live bacteria. These multi-electron exchanges modulate their free-carrier concentration, thus changing their plasmonic optical properties. This redoxresponsive plasmon absorbance can be modeled to provide quantitative analysis of electron transfer in systems out of redox equilibrium. wileyonlinelibrary.com

Luminescence, Plasmonic, and Magnetic Properties of Doped Semiconductor Nanocrystals

“…The green line represents part of electromagnetic wave applied on the nanocrystal. [13] respectively. c) UV/Vis-NIR absorption spectra showing Sn 4+ -doping induces aL SPR band in the near-to-mid IR region.…”

“…However,t he most successful and widely reported doping is the growth doping ( Figure 1b)i nw hich the doping process is decoupled from the host nucleation and dopants are allowed to adsorb on appropriate facets during the growth stage.T oo bserve emission exclusively from dopants,dopant ions are allowed to nucleate first ( Figure 1c); this approach has been found to be highly successful for both Mn and Cu doping. While all these synthetic processes were reported on different-sized host nanocrystals, recent process on precise control over doping and also digital doping were reported in which transition-metal ion dopants were placed successfully in molecular clusters (Figure 1f,g) including (CdSe) 13 .Hence,unlike adecade ago,the chemical doping of ac olloidal semiconductor nanocrystal is now largely understood. [23] Cu doping in CdSe has been achieved success- fully following this approach.…”

“…[25] It has been further observed that other dopants,such as Cr III and Ni II ,i nC d-Zn-S nanocrystals can also introduce mid-gap states and provide tunable emissions, [22b,d] though these are not as widely investigated as dopant Cu. [15b] However,a ss tated above,t he doping is achieved digitally [15b] and even precisely in as mall cluster.F igure 1l presents atypical case of UV/Vis,photoluminescence excitation (PLE) and photoluminescence (PL) spectra of Mn doped (CdSe) 13 crystals.I th as been suggested that this Mn d-d emission is tunable over am uch wider wavelength window than previously observed and this is one of the exciting observations on Mn doping. [22d] In comparison to Cu I ,a ll these dopants result high energy emissions.From the mechanistic study,itwas established that the Cu state remains mostly close to the valence band of the host and it behaves more like ternary CuInS 2 nanocrystals.…”

“…[11] Thec apability to modulate this LSPR band with small variations in the density of delocalized electrons gives rise to applications,s uch as near infrared (NIR)selective smart windows [12] and optical sensing [13] of electrochemical processes.A part from electronic, optical, and optoelectronic properties,e fforts are also being made to achieve useful magnetic properties by doping transition-metal ions with unpaired electrons in various compound semiconductor nanocrystals. Collective oscillation of these doped conduction electrons upon photo absorption yields localized surface plasmon resonance (LSPR) in doped nanocrystals.…”

“…Collective oscillation of these doped conduction electrons upon photo absorption yields localized surface plasmon resonance (LSPR) in doped nanocrystals. [11] Thec apability to modulate this LSPR band with small variations in the density of delocalized electrons gives rise to applications,s uch as near infrared (NIR)selective smart windows [12] and optical sensing [13] of electrochemical processes.A part from electronic, optical, and optoelectronic properties,e fforts are also being made to achieve useful magnetic properties by doping transition-metal ions with unpaired electrons in various compound semiconductor nanocrystals. [3c, 14] This Review highlights various recent developments in the field of doped colloidal semiconductor nanocrystals.Prior to discussing various properties, ab rief generic overview about the synthesis of these doped nanocrystals is provided.…”