A ratiometric fluorescent pH probe, 4-carboxylaniline-5-chlorosalicylaldehyde Schiff base (1) was synthesized via a facile reaction and used for pH sensing in live cells. While exhibiting weak fluorescence when dispersed in solution, 1 displayed aggregation-induced emission enhancement (AIEE) characteristics in its aggregate/solid state, as a result of the restriction of free intramolecular rotation of a C-N bond and the non-planar configuration in the aggregate/solid state. The integration of hydroxyl and carboxyl groups provided 1 with a ratiometric fluorescent response to pH based on AIEE and the pH-dependent spectral characteristics of compound 1, with proton dissociation constants pK a1 and pK a2 of 4.8 AE 0.1 and 7.4 AE 0.1, respectively. The probe exhibited a significant fluorescence color change from orange to green with an intensity ratio (I 516 nm / I 559 nm ) enhanced when the pH increased from 5.0 to 7.0 in aqueous solution. Confocal fluorescence imaging of intracellular pH through ratiometric response was successfully achieved in live HepG2 cells. The results demonstrate that probe 1 is a good candidate for monitoring pH fluctuations in live cells with good selectivity, stability, and excellent membrane permeability.

DNA–protein conjugates are very useful in analytical chemistry for target recognition and signal amplification. While a number of methods for conjugating DNA with proteins are known, methods for purification of DNA–protein conjugates from reaction mixture containing unreacted proteins are much less investigated. In this work, a simple and efficient approach to purify DNA–invertase conjugates from reaction mixture via a biotin displacement strategy to release desthiobiotinylated DNA–invertase conjugates from streptavidin-coated magnetic beads was developed. The conjugates purified by this approach were utilized for quantitative detection of cocaine and DNA using a personal glucose meter through structure-switching DNA aptamer sensors and competitive DNA hybridization assays, respectively. In both cases, the purified DNA–invertase conjugates showed better performance compared to the same assays using unpurified conjugates. The approach demonstrated here can be further expanded to other DNA and proteins to generate purified DNA–protein conjugates for analytical and other applications.

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In recent years, fluorescent organic compounds have rapidly expanded their applications in the fields of organic light-emitting diodes (OLED), photovoltaic devices, and photofunctional materials. 1 Particularly, dynamic altering and switching of solid-state luminescence of organic materials upon light, heat, pressure or other external factors, is attracting a spurt of interest. 2 Up to now, excellent examples of such organic materials have been reported. 3À6 For instance, Kato et al. has reported a shearinduced orderÀorder transition of liquid crystals (LC) accompanied with luminescence changing. 7 By incorporating spyropyran moieties to polymer bead, Davis' group also developed polymer materials with irreversible color change responding to stress-induced spiropyran reaction. 8 However, a major challenge in designing materials with tunable solid-state luminescence is the high-cost to synthesize the target compounds; also, a general principle for simply and efficiently developing such organic materials is still exceedingly needed.In this context, derivatives 1 (Scheme 1) substituted by N, N-diethylamino groups ((N,N-diethylamino)salicyaldehyde azine, DSA) attracted our attention. Featured by the simple preparation and high quantum yields in the solid state, 1 displayed tunable solid-state luminescence through the change of molecular packing modes during the mechanical grinding or annealing process. The morphology dependence of solid-state fluorescence properties was studied, and the structureÀproperty relationship was investigated. The mechanical-or heat-induced interconversion between the two crystals was found to be the reason for the switching the solid-state luminescence. In addition, a planar conjugated core attached by donorÀacceptor (DÀA) pairs might be a design principle for developing new organic materials with solid luminescence-switching properties.' RESULTS AND DISCUSSION Photophysical Properties of 1 in Solution. Figure 1 demonstrated the absorption and emission spectra of 1 in cyclohexane, THF, and DMSO solvents. The absorption of 1 was little affected by the solvent polarity, probably because the dipole moment of molecular ground and excited states is almost the same. 9 However, remarkable bathochromic shift could be observed as the solvent polarity was increased, with a pronounced enhancement in fluorescence intensity. These results are different from salicylaldehyde azine derivatives reported in our previous study, 10 which exhibited weak or no fluorescence when dissolved in solutions. These effects can be attributed to the incorporation of electron-donating N,N-diethylamino group to the electronwithdrawing salicylaldimine moiety, which leads to a DÀA pushÀpull pair and the corresponding intramolecular charge transfer (ICT) process in the solution state. 11Luminescence-Switching Properties of 1 in the Solid State. To investigate its solid-state fluorescence properties, the single crystal of 1 [DSA-1(Crys.)] was obtained with an orange color and a size around 0.5 Â 0.2 Â 0.1 cm by crystallizing fro...

In this work, two methods with complementary features, catalytic and molecular beacon (CAMB) and label-free fluorescent sensors using abasic site, have been combined into new label-free CAMB sensors that possess advantages of each method. The label-free method using dSpacer-containing molecular beacon makes CAMB more cost-effective and less interfering to the catalytic activity, while the CAMB allows the label-free method to use true catalytic turnovers for signal amplifications, resulting in a new label-free CAMB sensor for Pb2+ ion, with a detection limit of 3.8 nM while maintaining the same selectivity. Furthermore, by using CAMB to overcome the label-free method’s limitation of the requiring excess enzyme strand, a new label-free CAMB sensor using aptazyme is also designed to detect adenosine down to 1.4 μM, with excellent selectivity over other nucleosides.