gated imaging and nanocrystals-Katherine

Question 1

fingerprint treatments

Answer 1

long emission lifetime

sharp emission profiles

lanthanides absorb light with low efficiency, they are sensitised using an organic chromophore as ligand

absorbed energy is transferred to the lanthanide which then emits light

Question 2

gated imaging in 1979

Answer 2

fingerprint treatment leads to a luminescence lifetime substantially longer than a nanosecond, then turn on the imaging device after light source cut-off, with a delay such that the background fluorescence has already decayed, but luminescence is continuing

position of the camera defined the gate delay

fingerprint dusted with a powder terbium complex which luminesces with a lifetime on the order of a millisecond

limited in the speed of rotation of the cylinder, limits to fingerprint treatments that yield very long lifetimes

cannot arbitrarily scale up the size of the cylinder, as eventually the distance between camera and sample becomes too large to get good image resolution

Question 3

gated imaging mid 1980s

Answer 3

proximity-focused microchannel plate image intensifiers (MCP)

electronically turned on and off very rapidly, in times on the order of 10-8 seconds

Question 4

photoluminescent semiconductor nanocrystals

Answer 4

CdSe nanocrystals capped with zinc sulfide to reduce aggregation of the nanocrystals

bind to amino acids in fingerprint residue

Question 5

formulation for CdSe/ZnS/carboxylate functionalised nanocrystals

Answer 5

1uM of CdSe/ZnS/carboxylate functionalised nanocrystals left for 24 hours in solution

excitation from the ultraviolet to the red, which gives greater flexibility in terms of the excitation light source

sharp red luminescence was shown at 635nm

Question 6

absorption and emission spectra

Answer 6

absorption spectra of nanocomposites extremely broad, similar to bulk semiconductors

Question 7

fluorescent CdSe/ZnS stablised by octadecaneamine

Answer 7

fingermarks on silicon wafers or paper were immersed in a petroleum ether solution of CdSe/ZnS

detailed fluorescent prints were obtained on the silicon wafer specimens but fingermarks were not observed on paper due to heavy background fluorescence under UV illumination

Question 8

dendrimers

Answer 8

repetitively branched molecules

symmetric around the core, often adopts a spherical three-dimensional morphology

dendrimers separate and trap the nanoparticles limiting their aggression size

by controlling the chemical structure and size of the dendrimers, different size nanoclusters can be prepared

Question 9

nanoclusters

Answer 9

nanoclusters tailored by size to have luminescences ranging from blue to red, with sharp fluorescence peaks

by tailoring the size of the cluster, the luminescence lifetime is also altered but it remains in a range suitable for time-resolved work

CdS/generation 4 dendrimer solutions can be made up in methanol

absorption spectra indicated CdS nanocluster sizes of about 2.5nm

Question 10

diiminde enhancement

Answer 10

bonding of lipids of fingerprint material, to amine functional groups of dendrimers to form the amide linkage does not occur easily

diimides convert the carboxylic acid to an ester that more readily reacts with the amine functional group of the dendrimer