The photophysical properties of Nuc-DAOTA + (10 μM) in PBS (10 mM, pH 7.4) do not showed any significant changes during titrations with RNA (Figure , ESI) or BSA (Figure , ESI), even at higher concentrations up to 500 μg/mL. Thus, we can conclude that the addition of polar ammonium PEG motifs also effectively reduced the interactions of the probe with BSA, which is different from the previously reported water-soluble DAOTA + . However, significant changes to both the shape and maximum wavelength (λmax) of the absorption band were observed upon incremental addition of dsDNA to a solution of Nuc-DAOTA + (10 μM). Upon increasing the concentration of dsDNA from 0 to 150 μg/mL, the absorbance maxima at 557 nm red shifted to 570 nm (Δλmax ≈ 13 nm) with minor hyperchromic effect (Figure ). This red shift could be attributed to the change in the local polarity around the dye molecules from the hydrophilic medium to the hydrophobic environment created by the dsDNA, which in turn decreased the HOMO -LUMO energy gap of the probe. During titration with dsDNA, the merged shoulder absorbance band resulted from the initial different orientations of the dye molecules attained well defined sharp peak at 530 nm could be the reason of coplanar arrangement along with dsDNA molecules. A clear isosbestic point at 580 nm in the absorbance spectra indicates the formation of an equilibrium between the free probe and the Nuc-DAOTA + + dsDNA complex. The bathochromic shift in the absorbance maximum is clearly observed in the normalized absorbance spectra (Figure ). Upon excitation at 520 nm, the Nuc-DAOTA + (10 μM) showed fluorescence maxima at 590 nm, which displayed uniform increase in the fluorescence intensity accompanied by a minor blue shift (ΔλFI ≈ 5 nm), with gradual addition of dsDNA. The addition of dsDNA up to 50 μg/mL resulted in a notable enhancement of the fluorescence intensity calculated to be 38% with saturation (Figure , inset). The blue shift in the fluorescence maxima was more clearly shown in the normalized fluorescence spectra (Figure ). Compared to the previously reported binding constant of 4.5 x 10 5 M -1 between the DAOTA-M2 and dsDNA , the increased hydrophilicity of Nuc-DAOTA + from PEG-type chains resulted in a weaker binding affinity. The change in the fluorescence intensity (F -F0) as a function of dsDNA (μg/mL) concentration, exhibited an excellent linear correlation (R 2 = 0.999) within the range of 0 -50 μg/mL and a limit of detection (LOD) was found to be 0. The corresponding increase in the fluorescence lifetime upon addition of dsDNA could be due to the increased rigidity experienced by the dye molecules in the complex environment of the DNA molecules. The optical properties of Nuc-DAOTA + were also investigated in the presence of ssDNA under identical experimental conditions and resulted in more or less similar spectrophotometric and spectrofluorometric responses as that of dsDNA but comparatively required higher concentrations of ssDNA. The Nuc-DAOTA + showed weaker affinity for the ssDNA with binding constant (Kb) of 9.96 x 10 3 M -1 , calculated from the B-H plot between 1/(F-F0) and 1/ssDNA (Figure , ESI).