Fluorescence Screening of DNA-AgNCs with Pulsed White Light Excitation.

DNA-stabilized silver nanoclusters (DNA-AgNCs) are a class of fluorophores with interesting photophysical properties dominated by the choice of DNA sequence. Screening methods with ultraviolet excitation and steady state well plate readers have previously been used for deepening the understanding between DNA sequence and emission color of the resulting DNA-AgNCs. Here, we present a new method for screening DNA-AgNCs by using pulsed white light excitation (λ ≈ 490-900 nm).

Analytical method for the determination of the absorption coefficient of DNA-stabilized silver nanoclusters.

DNA-stabilized silver nanoclusters (DNA-AgNCs) are biocompatible emitters formed by silver atoms and cations encapsulated in DNA oligomers. Here, we present an analytical approach to calculate the molar absorption coefficient () of these systems, which consists of combining UV-Vis spectroscopy, electrospray ionization-mass spectrometry (ESI-MS), and inductively coupled plasma-optical emission spectrometry (ICP-OES). ESI-MS enables the determination of the number of silvers bound to the DNA strands, whereas ICP-OES allows measurement of the total amount of silver in solution.

Control of the fluorescence lifetime in dye based nanoparticles.

Fluorescent dye based nanoparticles (NPs) have received increased interest due to their high brightness and stability. In fluorescence microscopy and assays, high signal to background ratios and multiple channels of detection are highly coveted. To this end, time-resolved imaging offers suppression of background and temporal separation of spectrally overlapping signals.

Time gated Fourier transform spectroscopy with burst excitation for time-resolved spectral maps from the nano- to millisecond range.

We demonstrate burst-mode Time Gated Fourier Transform Spectroscopy (bmTG-FTS), a technique for simultaneously capturing and disentangling emission signals from short- (ns) and long-lived (μs-ms) states. We showcase the possibilities of the technique by preparing time gated temporal-spectral maps from a dual-emissive DNA-stabilized silver nanocluster (DNA-AgNC).

A DNA-Stabilized Ag Cluster with Excitation-Intensity-Dependent Dual Emission.

DNA-stabilized silver nanoclusters (DNA-AgNCs) are easily tunable emitters with intriguing photophysical properties. Here, a DNA-AgNC with dual emission in the red and near-infrared (NIR) regions is presented. Mass spectrometry data showed that two DNA strands stabilize 18 silver atoms with a nanocluster charge of 12+.

Bioconjugation of a Near-Infrared DNA-Stabilized Silver Nanocluster to Peptides and Human Insulin by Copper-Free Click Chemistry.

DNA-stabilized silver nanoclusters (DNA-AgNCs) are biocompatible emitters with intriguing properties. However, they have not been extensively used for bioimaging applications due to the lack of structural information and hence predictable conjugation strategies. Here, a copper-free click chemistry method for linking a well-characterized DNA-AgNC to molecules of interest is presented.

DNA-AgNC Loaded Liposomes for Measuring Cerebral Blood Flow Using Two-Photon Fluorescence Correlation Spectroscopy.

Unraveling the transport of drugs and nanocarriers in cerebrovascular networks is important for pharmacokinetic and hemodynamic studies but is challenging due to the complexity of sensing individual particles within the circulatory system of a live animal. Here, we demonstrate that a DNA-stabilized silver nanocluster (DNA-AgNC) that emits in the first near-infrared window upon two-photon excitation in the second NIR window can be used for multiphoton fluorescence correlation spectroscopy for the measurement of cerebral blood flow rates in live mice with high spatial and temporal resolution. To ensure bright and stable emission during experiments, we loaded DNA-AgNCs into liposomes, which served the dual purposes of concentrating the fluorescent label and protecting it from degradation.

Analysis of Compositional Bias in a Commercial Phage Display Peptide Library by Next-Generation Sequencing.

The principal presumption of phage display biopanning is that the naïve library contains an unbiased repertoire of peptides, and thus, the enriched variants derive from the affinity selection of an entirely random peptide pool. In the current study, we utilized deep sequencing to characterize the widely used Ph.DTM-12 phage display peptide library (New England Biolabs).

The effect of inosine on the spectroscopic properties and crystal structure of a NIR-emitting DNA-stabilized silver nanocluster.

The effect of replacing guanosines with inosines in the two stabilizing strands (5'-CACCTAGCGA-3') of the NIR emissive DNA-AgNC was investigated. The spectroscopic behavior of the inosine mutants is position-dependent: when the guanosine in position 7 was exchanged, the nanosecond fluorescence decay time shortened, while having the inosine in position 9 made the decay time longer. Thanks to structural information gained from single crystal X-ray diffraction measurements, it was possible to propose a mechanistic origin for the observed changes.

DNA Stabilizes Eight-Electron Superatom Silver Nanoclusters with Broadband Downconversion and Microsecond-Lived Luminescence.

DNA oligomers are known to serve as stabilizing ligands for silver nanoclusters (Ag-DNAs) with rod-like nanocluster geometries and nanosecond-lived fluorescence. Here, we report two Ag-DNAs that possess distinctly different structural properties and are the first to exhibit only microsecond-lived luminescence. These emitters are characterized by significant broadband downconversion from the ultraviolet/visible to the near-infrared region.

Probing emission of a DNA-stabilized silver nanocluster from the sub-nanosecond to millisecond timescale in a single measurement.

A method for measuring emission over a range of sub-nanosecond to millisecond timescales is presented and demonstrated for a DNA-stabilized silver nanocluster (DNA-AgNC) displaying dual emission. This approach allows one to disentangle the temporal evolution of the two spectrally overlapping signals and to determine both the nano- and microsecond decay times of the two emission components, together with the time they take to reach the steady-state equilibrium. Addition of a second near-infrared laser, synchronized with a fixed delay, enables simultaneous characterization of optically activated delayed fluorescence (OADF).

The effect of deuterium on the photophysical properties of DNA-stabilized silver nanoclusters.

We investigated the effect of using DO HO as solvent on the spectroscopic properties of two NIR emissive DNA-stabilized silver nanoclusters (DNA-AgNCs). The two DNA-AgNCs were chosen because they emit in the same energy range as the third overtone of the O-H stretch. Opposite effects on the ns-lived decay were observed for the two DNA-AgNCs.

Frequency Encoding of Upconversion Nanoparticle Emission for Multiplexed Imaging of Spectrally and Spatially Overlapping Lanthanide Ions.

We present frequency encoded upconversion (FE-UPCON) widefield microscopy, an imaging approach that allows for multiplexed signal recovery based on frequency encoding of selected upconverted lanthanide ion emission rather than separation based on energy or time. FE-UPCON allows for the separation of luminescence from spectrally and spatially overlapping trivalent lanthanide ions (Ln) in upconversion nanoparticles (UCNPs). Utilizing the numerous electronic energy levels of Ln, one can generate a frequency encoded signal by periodic coexcitation with a secondary light source (modulated at a chosen frequency) that, for a particular wavelength, enhances the luminescence of the Ln of interest.

Observation of microsecond luminescence while studying two DNA-stabilized silver nanoclusters emitting in the 800-900 nm range.

We investigated two DNA-stabilized silver nanoclusters (DNA-AgNCs) that show multiple absorption features in the visible region, and emit around 811 nm (DNA811-AgNC) and 841 nm (DNA841-AgNC). Both DNA-AgNCs have large Stokes shifts and can be efficiently excited with red light. A comparison with the commercially available Atto740 yielded fluorescence quantum yields in the same order of magnitude, but a higher photon output above 800 nm since both DNA-AgNCs are more red-shifted.

Single-Molecule Detection of DNA-Stabilized Silver Nanoclusters Emitting at the NIR I/II Border.

The near-infrared (NIR) I and II regions are known for having good light transparency of tissue and less scatter compared to the visible region of the electromagnetic spectrum. However, the number of bright fluorophores in these regions is limited. Here we present a detailed spectroscopic characterization of a DNA-stabilized silver nanocluster (DNA-AgNC) that emits at around 960 nm in solution.

Unusually large fluorescence quantum yield for a near-infrared emitting DNA-stabilized silver nanocluster.

A near-infrared emitting DNA-stabilized silver nanocluster (DNA-AgNC) with an unusually high fluorescence quantum yield is presented. The steady-state and time-resolved fluorescence properties of the DNA-AgNC were characterized, together with its ability to generate optically activated delayed fluorescence (OADF) and upconversion fluorescence (UCF).

Conformationally controlled ultrafast intersystem crossing in bithiophene systems.

Bithiophenes serve as model systems for larger polythiophenes used in solar cell applications and molecular electronics. We report a study of ultrafast dynamics of two bithiophene systems measured with femtosecond time-resolved photoelectron spectroscopy, and show that their intersystem crossing takes place within the first few picoseconds after excitation, in line with previous studies. We show that the intersystem crossing rate can be explained in terms of arguments based on symmetry of the S1 minimum energy geometry, which depends on the specific conformation of bithiophene.