Soluble Polymeric Dual Sensor for Temperature and pH Value

Abstract

The interest in "smart" functional materials that respond to changes in the environment strongly increased in the last years owing to the desire to control complexity and to create systems that adapt or respond to the environment. Moreover, such "smart" materials are used to design and develop new responsive materials for a wide range of applications in various fields, such as biotechnology, [1][2][3] drug delivery, [4][5][6] particle transport, [7] and optical sensing. [8][9][10][11] Recently, a thermoresponsive fluorescent nanogel was applied as an intracellular thermometer, that is, to monitor the temperature in living cells. [12] A current trend in the field of optical sensing is the development of dual sensors that respond simultaneously and independently to different stimuli. [13] In recent years, dual optical sensors have been reported for pressure and temperature, [14] oxygen and temperature, [15][16][17][18] oxygen and carbon dioxide, [19][20][21] as well as oxygen and pH value. [22][23][24] Surprisingly, no dual sensor has been reported for temperature and pH value, which would be beneficial, for example to monitor chemical reactions and for biological diagnostics.We have aimed to develop a soluble dual sensor that responds to both temperature and pH value. The solubility of the sensor material allows monitoring in situ while at the same time providing information about homogeneity and local conditions. In contrast to reported dual sensors, which are generally based on two different sensing chromophores, we have combined a pH-responsive solvatochromic dye with a thermoresponsive polymer. Solvatochromic dyes change color in response to changes in solvent polarity. [25][26][27] Recently, it was reported that combining a solvatochromic dye with a temperature-responsive polymer leads to a color change upon changing the temperature, as in the dissolved state the dye is in contact with water while in the collapsed state the dye is dissolved in the less polar precipitated polymer. [8][9][10]12] Herein, we report our efforts to develop a dual sensor that senses temperature by the solubility transition of a thermoresponsive polymer and senses the pH value by a pHresponsive solvatochromic dye, namely disperse red 1 (DR1, 1; Scheme 1). [28,29] Poly(oligoethyleneglycol methacrylate) (POEGMA) was chosen as temperature sensing polymer on the basis of its biocompatibility and the possibility of tuning the lower critical solution temperature (LCST) by copolymerizing different OEGMA monomers. [30][31][32] Since the polymer solubility transition can depend on the molar mass distribution of the copolymer, a well-defined polymer is required to ensure homogeneous solubility of the sensing polymer. Therefore, a controlled radical polymerization process, namely reversible addition fragmentation chain transfer (RAFT), [33][34][35] was applied to prepare welldefined copolymers of OEGMA and a methacrylate monomer functionalized with disperse red 1 (DR1-MA, 3; Scheme 1).For this purpose monomer 3 was prepared by esterification of...

Living Radical Polymerization by the RAFT Process – A Third Update

“…It has been reported that the extent of branching is higher 289 [186,187,229,577] 290 [175,203,305] 291 [211] 295 [308] 301 [165] 306 CSSQMA [389] 302 [164] 303 [209] 304 [305] 307 [578,579] 308 [579] 305 [212] 297 [188] 298 [201] 299 [201] 300 [387] 292 [189] 293 [173] 294 [210] Glycerol monomethacrylate Solketal methacrylate 296 [197,390] for conventional radical polymerization than for RDRP (ATRP, RAFT, and NMP). [443] A qualitative explanation was proposed in terms of the differences in the concentrations of short-chain radicals between RDRP and conventional radical polymerization.…”

Temperature Induced Solubility Transitions of Various Poly(2-oxazoline)s in Ethanol-Water Solvent Mixtures

“…The response of the "smart" material to the external triggering event can be manifold too, ranging from surface energy switching [10,19], a shape change [20], variation in absorption or emission [12], or the material can undergo a phase transition [15,18]. "Smart" polymeric materials that undergo a phase-transition in water are in particular interesting for the development of responsive solutions, e.g., for the development of diagnostic tools and sensors [21][22][23]. The majority of such temperature induced solubility transitions are based on the lower critical solution temperature (LCST) behavior of polymers in aqueous solution, i.e., the polymer is dissolved at low temperature by favorable hydration while increasing the temperature leads to an entropy driven dehydration resulting in a collapse of the hydrophobic polymer chains [18,21,23].…”

“…"Smart" polymeric materials that undergo a phase-transition in water are in particular interesting for the development of responsive solutions, e.g., for the development of diagnostic tools and sensors [21][22][23]. The majority of such temperature induced solubility transitions are based on the lower critical solution temperature (LCST) behavior of polymers in aqueous solution, i.e., the polymer is dissolved at low temperature by favorable hydration while increasing the temperature leads to an entropy driven dehydration resulting in a collapse of the hydrophobic polymer chains [18,21,23]. Polymers exhibiting the opposite upper critical solution temperature (UCST) behavior in aqueous solutions, i.e., insoluble at low temperatures and soluble at elevated temperatures, are much less common [24][25][26].…”

Thermometry at the nanoscale

“…The multi-optical response of the system to temperature, pH, oxygen content and saline conditions may constitute a drawback since the temperature response may be hindered by the change in other parameters but it is also an opportunity to design multiresponsive logic devices. 156,157 Polymer-based thermometers have the advantage of having higher sensitivities if only a narrow range (typically around room temperature) is requested. Also, these polymers can be designed as biocompatible beads, which is of fundamental importance for in vivo applications.…”