Upconverting Nanoparticle Relays for Resonance Energy Transfer Networks

Abstract

wileyonlinelibrary.comvariety of mechanisms such as DNA strand displacement, [ 3,[6][7][8] excited singlet saturation, [ 9,10 ] and optochemically accessed dark states of standard chromophores. [11][12][13][14][15][16][17] To store state in these networks, researchers have developed RET based fl ip-fl ops [ 16 ] and write-once polychromatic RET based storage devices with densities 1000 times greater than current standards. [ 18 ] Tying all of these circuit elements together is an impressive array of RET wires that can transport excitons through geometrically complex DNA nanostructures spanning more than 20 nm in length. [19][20][21][22][23][24] Given these extensive contributions, it is clear that the foundations for building more complex RET circuits have already been established.Despite these advances in essential circuit elements, the intrinsic energy loss of these networks currently prohibits large scale circuit fabrication. Energy loss is defi ned as the red-shifting Stokes effect that excitons incur as they traverse a set of RET donor-acceptor pairs. Once in the excited state, vibrational relaxation forces each fl uorophore's emission spectrum to be red-shifted with respect to its excitation spectrum. This shift requires an acceptor's excitation spectrum be lower in energy than its donor. Accordingly, as an exciton traverses any RET network from input to output it loses energy. Without a way to restore this energy, the output of one network cannot act as the input to a subsequent network, thereby prohibiting the cascading of independently designed RET networks to form larger circuitry. In certain cases, it may be possible to design an entire set of cascaded logic operations as a single RET network ensuring that the design does not violate this downhill energy fl ow; however, such solutions cannot be scaled to fabricate arbitrarily large circuits. Instead, we have engineered a device that will restore the energy of the excitons as they transition from one network to the next. This concept is analogous to a buffer in digital logic that decouples two networks and restores the signal between them. To achieve this restoration, we explored the use of upconversion.Upconverting processes combine many low energy inputs to form high energy outputs. The most commonly utilized upconversion processes rely entirely on far-fi eld interactions, e.g., multiphoton excitation of fl uorophores or excited state absorption in upconverting laser media. Such far-fi eld mechanisms, however, are unfi t for restoring energy in RET Networks of fl uorophores arranged at the nanoscale can perform basic computation using resonance energy transfer (RET) to transport and manipulate information in the form of excitons. As excitons travel through RET circuits, they are red-shifted due to vibrational energy loss at each transfer event. This loss prohibits RET circuits from being cascaded to form larger, more computationally complex systems. To address this issue, a nanoassembly capable of converting three or more low energy excitons into a si...

Recent progress in upconversion luminescence nanomaterials for biomedical applications

“…The excitation state of dyes at S1 will then transfer the energy to the sensitizers, such as Yb 3+ and a Nd 3+ -Yb 3+ pair through Föster and Dexter energy transfer. [44][45][46] Accepting the energy from dyes, the sensitizers are excited, followed by the energy transfer to activators for upconversion emission.…”

Energy Transfer Networks within Upconverting Nanoparticles Are Complex Systems with Collective, Robust, and History-Dependent Dynamics

“…5,[11][12][13] Recently, careful engineering of core-shell UCNP heterostructures has enabled them to be imaged at NIR laser power densities nine or more orders of magnitude lower than with two-photon fluorescence. [13][14] Beyond biological applications, UCNPs have spawned technologies in nanoscale thermometry [15][16] and viscometry, 17 anti-counterfeit labeling, 18 microscale lasers, [19][20] plasmonics, 21 photonic networks, 22 and photovoltaics. 23 Expanding UCNP applications depends largely on increasing upconversion efficiencies, which requires a deeper understanding for how lanthanide excited states dynamically interact.…”

Energy Transfer in Dye‐Coupled Lanthanide‐Doped Nanoparticles: From Design to Application

“…Apart from Yb 3+ ‐sensitized upconversion NPs, dye‐sensitized upconversion in Nd 3+ ‐sensitized NPs has also been demonstrated . Furthermore, an upconverting NP relay network was demonstrated by incorporating energy transfer from Cyto 840 dye to NaYF 4 :Yb/Tm, then subsequently to ATTO 448 to generate ATTO 488 emission light (Figure c) …”

“…[38] Furthermore, an upconverting NP relay network was demonstrated by incorporating energy transfer from Cyto 840 dye to NaYF 4 :Yb/Tm, then subsequently to ATTO 448 to generate ATTO 488 emission light (Figure 9c). [39] For bare core upconversion NPs, the luminescence efficiency is constrained by strongs urface quenchingc aused excitation depletion. This can be circumvented by coating an inert shell on the NP for conventionalu pconversion NPs.…”