Synthesis and characterization of ammonia-responsive polymer microgels

Abstract

aWe report a type of polymer microgels that undergo rapid, reversible, and highly sensitive volume phase transitions upon varying ammonia concentrations in milieu. Such an ammonia-responsive microgel is made by tethering of a phenoxazinium, N-(5-(3-azidopropylamino)-9H-benzo[a]-phenoxazin-9-ylidene)-N-methylmethanaminium chloride, to the network chains of poly(N-isopropylacrylamide-co-propargyl acrylate) via copper(I)-catalyzed azide-alkene cycloaddition. Tethering of the ammonia-recognizable phenoxazinium onto polymer network chains makes the microgels responsive to ammonia. While a fast (<0.1 s) and stable shrinkage of the microgels can be reached upon adding ammonia over a clinically relevant range (0.25−2.9 ppm), the microgels can convert the elevated concentrations of the solution-/gas-phase ammonia into enhanced photoluminescence signals, which make the microgels different from the phenoxazinium or its analogs reported in previous arts that exhibit ammonia-induced quenching in photoluminescence. With the microgels as probes, the detection limit was ca. 7.3×10 -2 and 3.9 ppb, respectively, for the solution-and the gas-phase ammonia. These features enable "turn-on" photoluminescence detection of ammonia in breath.

Assembly of polythiophenes on responsive polymer microgels for the highly selective detection of ammonia gas

“…S7 in ESI † for TEM image; 60-90 nm in diameter). 62 Since the polymer particles dehydrated, shrunk, flattened and spread on TEM grid during the sample preparation, individual microgels were not expected to interact with the substrate in a homogeneous fashion, leading to a larger apparent polydispersity. Thus, we also performed particle sizing on the AP-0.1 and ARM microgels via in situ DLS, a less disturbing method.…”

“…ARM microgels were synthesized according to a recent report by our group. 62 For preparing the composite materials, 30.0 mL of an aqueous dispersion of ARM microgels (50.0 μg mL −1 ) was stirred at room temperature for 30 min in a 100 mL round-bottom flask under N 2 purging. At the same time, P3ET solution (1.0 mg mL −1 in THF) was prepared by dissolving P3ET in THF.…”

“…The film thickness was measured three times with a micrometer, and the mean value was taken. The film conductivity was measured in an airproof chamber equipped with a gas-flow bench 62 using AC impedance spectroscopy (Solartron frequency analyser 1260) over the frequency range of 10 −3 -10 7 Hz using a four-electrode probe (BekkTech LLC). Platinum wires were used as the working/counter electrodes to apply a current to the sample, and two separate platinum wires were used as reference electrodes.…”

“…As a proof of concept, the proposed smart composite materials were prepared by the assembly of poly 62 The electron-withdrawing effect of the central N-atom in the oxazine of the phenoxazinium can cause the partial alkylated amino side groups to be more acidic, favouring the bonding of ARM with ammonia gas. 41,63 Under this design, the composite materials with the conjugated polymer assemblies immobilized on responsive polymer microgels combine the properties of both the conjugated polymer assemblies and responsive polymers, offering exceptional possibilities.…”

“…This makes the composite material different from the previously reported conductive polymer platforms that may also respond to non-ammonia gases with the response degree close to ammonia gas [54][55][56][59][60][61] and the template microgels that exhibit optical change only. 62 These features underlie the great potential of composite materials for applications related to ammonia detection.…”