Visualizing biomolecular and cellular processes inside intact living organisms is a major goal of chemical biology. However, existing molecular biosensors, based primarily on fluorescent emission, have limited utility in this context due to the scattering of light by tissue. In contrast, ultrasound can easily image deep tissue with high spatiotemporal resolution, but lacks the biosensors needed to connect its contrast to the activity of specific biomolecules such as enzymes. To overcome this limitation, we introduce the first genetically encodable acoustic biosensors—molecules that ‘light up’ in ultrasound imaging in response to protease activity. These biosensors are based on a unique class of air-filled protein nanostructures called gas vesicles, which we engineered to produce nonlinear ultrasound signals in response to the activity of three different protease enzymes. We demonstrate the ability of these biosensors to be imaged in vitro, inside engineered probiotic bacteria, and in vivo in the mouse gastrointestinal tract.

可视化完整生物体内的生物分子和细胞过程是化学生物学的一个主要目标。然而，由于组织对光的散射，现有的主要基于荧光发射的分子生物传感器在这方面的实用性有限。相比之下，超声波可以轻松地以高时空分辨率对深层组织进行成像，但缺乏将其对比度与酶等特定生物分子的活性联系起来所需的生物传感器。为了克服这一限制，我们引入了第一个可遗传编码的声学生物传感器——在超声成像中响应蛋白酶活性而“发光”的分子。这些生物传感器基于一类独特的充气蛋白质纳米结构，称为气泡，我们设计它以响应三种不同蛋白酶的活性产生非线性超声信号。我们证明了这些生物传感器在体外、工程益生菌内部和小鼠胃肠道体内成像的能力。