01/06/2019
TOP nanosensor made of a NIR-emissive chromium-(III) complex (blue), a pH indicator (green) and a reference dye (orange) in a 100 nm polymer particle

TOP nanosensor made of a NIR-emissive chromium-(III) complex (blue), a pH indicator (green) and a reference dye (orange) in a 100 nm polymer particle

Source: BAM, Division Biophotonics

Among the most relevant analytes for the environment, biotechnology, and the life and material sciences are temperature (T), oxygen (O) partial pressure, and pH (P), which can indicate e.g. corrosion processes and health-related problems. The need for materials and methodologies for simultaneously monitoring these parameters as simple, fast, and reliable as led to the DFG-financed development of new ratiometric optical nanosensors for TOP determination.

The key component of these TOP nanosensors is a luminescent chromium (III) complex, a “molecular ruby analogue”. This unique compound shows a strong and structured luminescence in the near infrared (NIR) region at about 780 nm upon excitation at 435 nm. This luminescence is sensitive to oxygen (change in intensity and lifetime) and temperature (change in intensity ratio). The extremely large energy gap between the absorption and emission band of the chromium (III) complex provides the basis for the construction of multianalyte sensors, as it enables the combination with several spectrally distinguishable fluorophores emitting within this energy gap. For the fabrication of the TOP nanosensors the hydrophobic chromium (III) complex and an analyte-insensitive reference dye with a spectrally well separated emission band were encapsulated in 100 nm-sized polystyrene nanoparticles using a simple swelling procedure. The particles were then sealed with a thin aminated silica shell to immobilize the luminophores within the nanoparticles. Subsequently, a pH-sensitive fluorescein derivative suited for pH-sensing in the biologically relevant pH range of 4.1 to 8.9 (pKa value of 6.5) was covalently bound to the aminated particle surface. The resulting TOP nanosensors are very stable in water, different buffers, and cell culture medium. Additionally, they reveal a fast and fully reversible ratiometric response to all TOP parameters and can be fabricated in different formats ranging from differently sized particles to sensor films. These TOP nanosensors are currently assessed for applications in cell studies and the monitoring of biotechnological and microbial-induced corrosion processes.

Luminescent TOP nanosensors for simultaneously measuring temperature, oxygen, and pH at a single excitation wavelength
Cui Wang, S. Otto, M. Dorn, K. Heinze, Ute Resch-Genger
Analytical Chemistry, 2019, Volume 91, pages 2337-2344
BAM, Department Analytical Chemistry; Reference Materials, Biophotonics Division