Direct profiling of tissue sections by MALDI mass spectrometry, using molecular imaging, is a powerful procedure to study the spatial distribution of large and small molecules directly from a biological matrix.
The depiction of mass spectral data images as two-dimensional images allows the spatial distribution of molecules to be determined visually. Unlike the time-consuming and costly traditional methods of spatial profiling, such as autoradiography and scintillation counting, radio-labeling are not required.
The MALDI SYNAPT G2-Si HDMS allows for the extraction of mass, intensity, and positional information, using a 200 Hz solid-state laser that delivers rapid data acquisition.
Extracted data can be imported into any suitable software package, such as BioMap (Novartis), for image generation and manipulation.
MALDI-based tissue imaging offers a complementary approach to established imaging techniques such as whole-body radiography. It does not require labeling of the compounds of interest, and multiple compounds can be monitored simultaneously.
Conventional MALDI Imaging
A limitation of imaging by conventional MALDI MS is the absence of a separation step prior to MS. Due to the complexity of tissue samples, this poses a major risk that isobaric ions will distort the ion distribution, thus invalidating results.
High Definition Imaging with MALDI HDMS
The extra dimension of separation provided by the MALDI SYNAPT HDMS System can be used to produce images without interference from background ions of similar mass, leading to more precise localization of a drug or metabolite of interest. Ions are separated using ion mobility (IMS) prior to mass analysis.
The images below show the distinction of a selected ion across a kidney section. The use of HDMS clearly helps to provide the true spatial tissue distribution of the endogenous metabolite of mass 402.01 Da by removing any contribution of the interfering matrix ion of mass 402.07 Da.
Ion image of m/z 402.01, without ion mobility separation.
Ion image of m/z 402.01 (ion of interest) with ion mobility separation. When the ion mobility range from 2.7 to 3.3 ms is combined, its ion image has a significantly lower background noise level.
Ion image of m/z 402.07 (interfering background ion) with ion mobility separation, with selected drift time 3.4 to 4.1 ms.