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. 2020 Dec 16;60(7):3619–3624. doi: 10.1002/anie.202009542

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© 2020 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH

This is an open access article under the terms of the http://creativecommons.org/licenses/by-nc-nd/4.0/ License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non‐commercial and no modifications or adaptations are made.

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Programming the t _lf, t _lag and pH_min of transient acidic pH flips: a) Increasing the c _esterase leads to a pronounced pH_min, longer t _lf and shorter t _lag. Conditions: h _esterase:h _urease=4:1, c _EA=c _urea=100 mM, c _esterase + c _urease=1.0 mg mL⁻¹, and 5 mM PBS (pH 7.0; 0.5 mg mL⁻¹ BSA; 20 °C). b) The t _lag is controlled by the buffer concentration. Conditions: h _esterase:h _urease=4:1, 0.7 mg mL⁻¹ esterase, 0.3 mg mL⁻¹ urease, c _EA=c _urea=100 mM, 0.5 mg mL⁻¹ BSA, and 20 °C. c) Adjusting the ratio of EA and urea results in a wide tuneability of t _lf and pH_min. Conditions: h _esterase:h _urease=4:1, 0.7 mg mL⁻¹ esterase, 0.3 mg mL⁻¹ urease, c _EA + c _urea=200 mM, and 5 mM PBS (pH 7.0; 0.5 mg mL⁻¹ BSA; 20 °C). d) The height ratio of esterase and urease layers regulates the pH_min, t _lf and t _lag. Conditions: 0.7 mg mL⁻¹ esterase, 0.3 mg mL⁻¹ urease, c _EA=c _urea=100 mM, and 5 mM PBS (pH 7.0; 0.5 mg mL⁻¹ BSA; 20 °C). e) Effects of installing a blank hydrogel layer between esterase and urease layers on the expense of the esterase layer thickness. Conditions: 0.7 mg mL⁻¹ esterase, 0.3 mg mL⁻¹ urease, c _EA=c _urea=100 mM, and 5 mM PBS (pH 7.0; 0.5 mg mL⁻¹ BSA; 20 °C). f) Effects of installing a blank layer while maintaining esterase and urease layer thickness. Conditions: 0.7 mg mL⁻¹ esterase, 0.3 mg mL⁻¹ urease, c _EA=c _urea=100 mM, and 5 mM PBS (pH 7.0; 0.5 mg mL⁻¹ BSA; 20 °C). (a′–f′) The corresponding pH_min, t _lag and t _lf of the transient acidic pH flips in (a–f). All data are an average of three measurements, detailed experimental conditions are listed in Table S2.