Leccese Silvia, Calcinoni Andrea, Wilson Adjélé, Kirilovsky Diana, Carbonera Donatella, Onfroy Thomas, Jolivalt Claude, Mezzetti Alberto
Sorbonne Université, CNRS, Laboratoire de Réactivité de Surface (LRS), 4 Place Jussieu, 75005 Paris, France.
Department of Chemical Sciences, University of Padova, 35131 Padova, Italy.
Micromachines (Basel). 2023 Sep 29;14(10):1871. doi: 10.3390/mi14101871.
Orange carotenoid protein (OCP) is a photochromic carotenoprotein involved in the photoprotection of cyanobacteria. It is activated by blue-green light to a red form OCP capable of dissipating the excess of energy of the cyanobacterial photosynthetic light-harvesting systems. Activation to OCP can also be achieved in the dark. In the present work, activation by pH changes of two different OCPs-containing echinenone or canthaxanthin as carotenoids-is investigated in different conditions. A particular emphasis is put on OCP encapsulated in SBA-15 mesoporous silica nanoparticles. It is known that in these hybrid systems, under appropriate conditions, OCP remains photoactive. Here, we show that when immobilised in SBA-15, the OCP visible spectrum is sensitive to pH changes, but such a colorimetric response is very different from the one observed for OCP in solution. In both cases (SBA-15 matrices and solutions), pH-induced colour changes are related either by orange-to-red OCP activation, or by carotenoid loss from the denatured protein. Of particular interest is the response of OCP in SBA-15 matrices, where a sudden change in the Vis absorption spectrum and in colour is observed for pH changing from 2 to 3 (in the case of canthaxanthin-binding OCP in SBA-15: λ shifts from 454 to 508 nm) and for pH changing from 3 to 4 (in the case of echinenone-binding OCP in SBA-15: λ shifts from 445 to 505 nm). The effect of temperature on OCP absorption spectrum and colour (in SBA-15 matrices) has also been investigated and found to be highly dependent on the properties of the used mesoporous silica matrix. Finally, we also show that simultaneous encapsulation in selected surface-functionalised SBA-15 nanoparticles of appropriate fluorophores makes it possible to develop OCP-based pH-sensitive fluorescent systems. This work therefore represents a proof of principle that OCP immobilised in mesoporous silica is a promising system in the development of colorimetric and fluorometric pH and temperature sensors.
橙色类胡萝卜素蛋白（OCP）是一种光致变色类胡萝卜素蛋白，参与蓝细菌的光保护作用。它被蓝绿光激活为红色形式的OCP，能够消散蓝细菌光合光捕获系统中多余的能量。在黑暗中也能实现对OCP的激活。在本工作中，研究了在不同条件下，通过改变pH值对两种含有不同类胡萝卜素（海胆酮或角黄素）的OCP的激活情况。特别强调了封装在SBA - 15介孔二氧化硅纳米颗粒中的OCP。已知在这些混合体系中，在适当条件下，OCP保持光活性。在此，我们表明，当固定在SBA - 15中时，OCP的可见光谱对pH值变化敏感，但这种比色响应与在溶液中观察到的OCP的响应非常不同。在两种情况下（SBA - 15基质和溶液），pH诱导的颜色变化要么与橙色到红色的OCP激活有关，要么与变性蛋白中类胡萝卜素的损失有关。特别有趣的是SBA - 15基质中OCP的响应，当pH从2变为3时（在SBA - 15中结合角黄素的OCP的情况下：波长从454 nm移至508 nm）以及当pH从3变为4时（在SBA - 15中结合海胆酮的OCP的情况下：波长从445 nm移至505 nm），观察到可见吸收光谱和颜色的突然变化。还研究了温度对OCP吸收光谱和颜色（在SBA - 15基质中）的影响，发现其高度依赖于所用介孔二氧化硅基质的性质。最后，我们还表明，将适当的荧光团同时封装在选定的表面功能化SBA - 15纳米颗粒中，使得开发基于OCP的pH敏感荧光系统成为可能。因此，这项工作证明了固定在介孔二氧化硅中的OCP在开发比色和荧光pH及温度传感器方面是一个有前途的系统。
