Project SIREN – Development of the next generation of SWIR emitting probes for bioimaging

23/08/2023

• Challenge
• Objectives
• Methods
• Partners

Biomedical applications of optical imaging have been extensively developed over the last years. Challenges for sensitive bioimaging with fluorescence techniques are a high penetration depth, high contrast, and high spatial resolution, which are hampered by light scattering, absorption, and tissue autofluorescence. Therefore, new contrast agents with an emission in the short-wavelength infrared (SWIR) (900-1700 nm) are required, which have a high absorption and a high luminescence quantum yield.

In the project SIREN, BAM and IAB will design and synthesize bright SWIR emitters from gold nanoclusters (AuNCs) and heavy metal-free Ag₂S quantum dots (QDs) and explore their optical properties, particularly their luminescence quantum yields and brightness. Signal-relevant spectroscopic key features will be compared with models (optical phantoms) and bioimaging studies. Also, tools and test materials will be developed to standardize SWIR luminescence measurements.

BAM and IAB will develop new synthesis strategies for preparing bright gold nanoclusters and water-soluble Ag₂S quantum dots. The aim is to optimize the luminescence and brightness by exploring the critical synthesis parameters of each nanomaterial and control its growth. Quantitative luminescence measurements with calibrated fluorescence spectrometers at BAM and imaging setups in France will provide the basis for standardizing fit-for-purpose SWIR contrast agents for bioimaging.

Consortium:
Joint research project with the Institute for Advanced Biosciences (IAB) Grenoble, France

Funding:
Financial support from DFG and ANR (DFG grant RE 1203/38-1; ANR-20-CE92-0039-01).

Current challenges of non-invasive optical bioimaging are to realize a deep tissue penetration with a high detection sensitivity, a high spatial and temporal resolution, and fast data acquisition. A promising spectral window to tackle these challenges is the short-wavelength infrared (SWIR) between about 900-1700 nm where the scattering, absorption, and autofluorescence of tissue are strongly reduced compared to the visible (400–650 nm) and NIR (~700–900 nm). SWIR exploitation is currently hampered by a lack of suitable optical contrast agents with a high photoluminescence (PL) quantum yield (QY) and a high brightness, that can be safely used in vivo, a lack of quantitative and reliable data on the signal-relevant optical properties of molecular and nanoscale SWIR emitters hampering emitter comparison and the rational design of new SWIR contrast agents, and a lack of fluorescence standards.

Aiming for providing the basis for sensitive and fast SWIR PL bioimaging (PLI), German and French experts in quantitative optical spectroscopy, photophysics, probe design, and optical imaging have joined forces to develop new SWIR contrast agents and advanced image analysis methods. Their tasks include the rational design of bright SWIR reporters utilizing atomically precise gold nanoclusters (AuNCs) and heavy metal-free quantum dots (QDs) like Ag₂S QDs with improved optical properties and their spectroscopic characterization in solution and in artificial models mimicking tissues to minimize the utilization of animal studies. Strategies to improve the detection sensitivity and resolution will be addressed by comparing different spectral windows in the SWIR, thus considering the wavelength-dependent absorption and scattering properties of tissue, preparing multimeric AuNCs to tune PL and brightness, and fine-tuning Ag₂S synthesis and surface chemistry. In parallel, SWIR spectral multiplexing with these emitters will be explored.

Quantitative, accurate, and reliable data on signal-relevant spectroscopic key features of different SWIR reporters will be obtained with the calibrated fluorescence spectrometers at BAM in organic solvents, aqueous buffers, and biologically relevant environments. Best performing and “biologically safe” contrast agents will be further evaluated in bioimaging studies to determine their potential for SWIR PLI of organ vascularization by the French partner. Spatial resolution and signal-to-noise ratios will be quantified, using different methods of image analysis and enhancing the PL data information content. The spectroscopic features and probe performance in SWIR PLI, (SWIR signal size) will be correlated and used to derive probe design criteria. The gained knowledge will be used to develop a concept for standardizing SWIR PL measurements including suitable reference materials. This will complement the platform of reference materials for PL and QY and the spectral fluorescence standards for the UV/vis/NIR of BAM.

Partner

Institute for Advanced Biosciences (IAB), Grenoble, France

Förderung

ANR-DFG Förderprogramm