Ultra‐Bright Near‐Infrared Sulfonate‐Indolizine Cyanine‐ and Squaraine‐Albumin Chaperones: Record Quantum Yields and Applications

Abstract

The Front Cover shows a single near‐infrared dye being laser‐excited and dimly fluorescing in an aqueous biological environment compared to a near‐infrared dye bound to albumin fluorescing brightly in the same environment. Cover designed by Karina Kapusta. Read the full text of the Research Article at 10.1002/cptc.202200127.

Switch-on near infrared emission in albumin behind dark fabric: toward application in forensic latent bloodstain detection

“…S9†, and SO3SQ ) were rigorously studied via computational protein docking. 12 In that study, the dyes were found to bind primarily to the heme cleft of HSA. A significant contributor in binding was the sulfonate indolizine moiety where both the indolizine heterocycle and sulfonate group appended to the heterocycle had distinct protein group binding.…”

“…Our group has previously reported an indolizine squaraine dye ( SO3SQ , Scheme 1) that demonstrates “ultra-bright” switch-on near infrared (NIR, 700–1000 nm) emission upon binding to albumin in fetal bovine serum (FBS), human serum albumin (HSA), and on latent blood stains. 11–13 Albumin has previously been shown to enhance dye emission for sensors and for in vivo biological imaging; however, these reports have not been found to be applicable in forensic imaging (Table S2†). 9,14–25 The albumin– SO3SQ complex displays longer lived emission (on the order of days to weeks), more selectivity for blood (since albumin is specific to and ubiquitous in blood), 26,27 and leaves DNA less perturbed than with oxidizing solutions or ultraviolet (UV, 100–400 nm) light.…”

“…13 Upon binding to albumin, the dye most likely assumes a restricted conformation with fewer avenues for non-radiative decay and thus a brighter emission compared to water alone. 12,13,28 The NIR emission of SO3SQ ( λ emis max = 722 nm) extends beyond the absorption of UV and visible light (400–700 nm) by molecules like hemoglobin in the blood. 29 For this reason, NIR emission is preferred over the blue emission from luminol at 425 nm.…”

Latent bloodstain detection using a selective turn-on NIR fluorescence dye responsive to serum albumin

“…In these studies, cattle blood was used as the blood source since SO 3 SQ has shown the ability to detect both human and bovine albumin. 43…”

“…The enhancement in uorescence of SO 3 SQ may derive from the disaggregation of dyes 41,42 and subsequently binding of monomeric SO 3 SQ to albumin. 43 The change in environment aer complexation with the HSA protein might also promote the high uorescent emission. To the best of our knowledge, there is no report on the latent bloodstain detection using NIR uorescent dyes with turn-on uorescent intensity enhancements.…”