A comprehensive review on LED-induced fluorescence in diagnostic pathology.

Sensitivity, specificity, mobility, and affordability are important criteria to consider for developing diagnostic instruments in common use. Fluorescence spectroscopy has been demonstrating substantial potential in the clinical diagnosis of diseases and evaluating the underlying causes of pathogenesis. A higher degree of device integration with appropriate sensitivity and reasonable cost would further boost the value of the fluorescence techniques in clinical diagnosis and aid in the reduction of healthcare expenses, which is a key economic concern in emerging markets. Light-emitting diodes (LEDs), which are inexpensive and smaller are attractive alternatives to conventional excitation sources in fluorescence spectroscopy, are gaining a lot of momentum in the development of affordable, compact analytical instruments of clinical relevance. The commercial availability of a broad range of LED wavelengths (255-4600 nm) has opened up new avenues for targeting a wide range of clinically significant molecules (both endogenous and exogenous), thereby diagnosing a range of clinical illnesses. As a result, we have specifically examined the uses of LED-induced fluorescence (LED-IF) in preclinical and clinical evaluations of pathological conditions, considering the present advancements in the field.

Probing nonenzymatic glycation of proteins by deep ultraviolet light emitting diode induced autofluorescence.

The suitability of deep-UV-LED (285 nm) as an excitation source to induce autofluorescence in nonenzymatically glycated proteins has been reported for the first time in this study. Non-enzymatically glycated proteins show high autofluorescence when excited with deep-UV light, i.e., deep-UV-induced autofluorescence (deep-UV-IAF). Multiple autofluorescence peaks of nonenzymatically glycated proteins between 300 and 600 nm when excited using the deep-UV-LED revealed structural and biochemical modifications. The partial unfolding of proteins in which Tryptophan (Trp) is either absent (e.g., RibonucleaseA) or the emission maxima of Trp is insensitive to nonenzymatic glycation (e.g., Human Serum Albumin and Bovine Serum Albumin) were elucidated using their Tyrosine (Tyr) emission (λem = ~320 nm). Also, the deep-UV-LED-induced autofluorescence (deep-UV-LED-IAF) is shown to detect and track a wide range of clinically relevant advanced glycation end-products (AGEs) such as Pentosidine (λem = ~380 nm), Argpyrimidine (λem = ~395 nm), Vesperlysine C (λem = ~405 nm), Vesperlysine A/B (λem = ~440 nm), Crossline (λem = ~480 nm), and Arginine derived AGEs (λem = ~525 nm) which is also supported by the chemometric analysis (PCA). The relevance of Trp/Tyr makeup of proteins in tracking AGEs using deep-UV-IAF has been carefully examined with proteins such as RibonucleaseA (RNaseA:zero Trp and six Tyr), Human Serum Albumin (HSA: one Trp and eighteen Tyr), Bovine Serum Albumin (BSA: two Trp and twenty Tyr) and Hemoglobin (Hb: four Trp and twelve Tyr). The Molecular Dynamic (MD) simulation revealed a high root-mean-square deviation (RMSD: 4.6 Å) and an increased average distance between Tyr residues and Trp214 (23.2 Å) in methylglyoxal (MG) treated HSA. This confirms the MG-induced protein unfolding and decreased fluorescence resonance energy transfer (FRET) from Tyr to Trp (Tyr â†’ Trp). The study also used systematic steady-state and time-resolved fluorescence (TRF) to explain the sudden decrease in AGEs specific fluorescence intensity and lifetime at higher concentrations of MG due to inter-AGEs FRET.