Comparative Analysis of Fluorescence Reporter Signals Based on Intensity, Anisotropy, Time-Resolution, and Wavelength-Ratiometry

Exploring Fluorescence Spectral Shifts in Aptamer-Intercalating Cyanine Dye Complexes upon Binding to Specific Small Molecules

DNA intercalating cyanine dyes, such as SYBR Green I (SG) and OliGreen (OG), are widely used in developing label-free, fluorescent aptamer-based biosensors. Despite their widespread use for direct analyte detection through changes in fluorescence intensity, the effects of dye concentrations and the specific nature of their interactions have been inadequately explored. Here, we reported how dye-to-base ratios (dbrs) influence the fluorescent response of DNA intercalating dyes in aptamer systems targeting adenosine triphosphate (ATP) and l-argininamide (LAA). We initially examined the fluorescence spectral shifts of an ATP aptamer (ABA) with SG across varying dbrs, observing an emission shift to longer wavelengths as the dbrs increased. Subsequently, systematic analysis of the ATP aptamer and SG complex (ABA/SG) at different target concentrations revealed a "signal-off" phenomenon at a very low dbr of 0.1, which transitioned to a blue shift in the fluorescence spectra at higher dbr values of 0.7 and 2.0. Further extending our research, we explored the use of OG as a ratiometric probe for detecting l-argininamide, noting similar spectral shifts to shorter wavelengths upon target binding. Absorption spectroscopy, circular dichroism (CD), and meticulously designed control studies were employed to elucidate the spectral shift phenomenon comprehensively. Our findings underscore the significant impact of dye selection and concentration on the performance of fluorescence aptasensors and demonstrate that clear spectral shifts, indicative of target binding, occur upon binding to targets, particularly at higher dye loading; however, excessive dye concentrations can perturb the aptamer structure, reducing its binding affinity. We believe that our findings will provide new insights into designing aptamer-based fluorescence assays for the sensitive and specific detection of small molecules.

Integration of an LPAR1 Antagonist into Liposomes Enhances Their Internalization and Tumor Accumulation in an Animal Model of Human Metastatic Breast Cancer

Lysophosphatidic acid receptor 1 (LPAR1) is elevated in breast cancer. The deregulation of LPAR1, including the function and level of expression, is linked to cancer initiation, progression, and metastasis. LPAR1 antagonists, AM095 or Ki16425, may be effective therapeutic molecules, yet their limited water solubility hinders in vivo delivery. In this study, we report on the synthesis of two liposomal formulations incorporating AM095 or Ki16425, embedded within the lipid bilayer, as targeted nanocarriers for metastatic breast cancer (MBC). The data show that the Ki16425 liposomal formulation exhibited a 50% increase in internalization by MBC mouse epithelial cells (4T1) and a 100% increase in tumor accumulation in a mouse model of MBC compared with that of a blank liposomal formulation (control). At the same time, normal mouse epithelial cells (EpH-4Ev) internalized the Ki16425 liposomal formulation 25% lesser than the control formulation. Molecular dynamics simulations show that the integration of AM095 or Ki16425 modified the physical and mechanical properties of the lipid bilayer, making it more flexible in these liposomal formulations compared with liposomes without drug. The incorporation of an LPAR1 antagonist within a liposomal drug delivery system represents a viable therapeutic approach for targeting the LPA-LPAR1 axis, which may hinder the progression of MBC.

Ratiometric Fluorescence Detection of Phosphorylated Amino Acids Through Excited-State Proton Transfer by Using Molecularly Imprinted Polymer (MIP) Recognition Nanolayers

A 2,3-diaminophenazine bis-urea fluorescent probe monomer (1) was developed. It responds to phenylphosphate and phosphorylated amino acids in a ratiometric fashion with enhanced fluorescence accompanied by the development of a redshifted emission band arising from an excited-state proton transfer (ESPT) process in the hydrogen-bonded probe/analyte complex. The two urea groups of 1 form a cleft-like binding pocket (K_b >10¹⁰  L²  mol^-2 for 1:2 complex). Imprinting of 1 in presence of ethyl ester- and fluorenylmethyloxycarbonyl (Fmoc)-protected phosphorylated tyrosine (Fmoc-pTyr-OEt) as the template, methacrylamide as co-monomer, and ethyleneglycol dimethacrylate as cross-linker gave few-nanometer-thick molecularly imprinted polymer (MIP) shells on silica core microparticles with excellent selectivity for the template in a buffered biphasic assay. The supramolecular recognition features were established by spectroscopic and NMR studies. Rational screening of co-monomers and cross-linkers allowed to single out the best performing MIP components, giving significant imprinting factors (IF>3.5) while retaining ESPT emission and the ratiometric response in the thin polymer shell. Combination of the bead-based detection scheme with the phase-transfer assay dramatically improved the IF to 15.9, allowing sensitive determination of the analyte directly in aqueous media.

A BODIPY/pyrene-based chemodosimetric fluorescent chemosensor for selective sensing of hydrazine in the gas and aqueous solution state and its imaging in living cells

A BODIPY-based pyrenebutyrate-linked (BPB) chromogenic and fluorogenic probe was synthesized and characterized for the specific detection of hydrazine.