MALDI stands for Matrix-Assisted Laser Desorption Ionization. TOF stands for Time of Flight. By Jwala Jayadeep KUFOS

1. MALDI- TOF MASS
SPECTROMETRY
BY JWALA
1st MSc MARINE MICROBIOLOGY

2. INTRODUCTION
 MALDI is a soft ionization technique that strikes large
molecules with laser energy into minimal ion fragments.
 MALDI stands for Matrix-
Assisted Laser Desorption Ionization.
 TOF stands for Time of Flight.
 This technology generates characteristic mass
spectral fingerprints which are compared
with large library of mass spectra. As the spectral
fingerprints are unique signatures for each
microorganism, accurate microbial identification at
the genus and species levels is done using
bioinformatics pattern profiling.

3. MALDI-TOF MASS SPECTROMETER

4. WORKING PRINCIPLE FOR MALDI-
TOF SPECTROMETRY
The MALDI-TOF process is a two-phase
procedure;
 Ionization Phase
 Time of flight phase
The second phase is the time-of-flight mass
spectrometry phase. It has two modes:- linear
mode and reflector mode.

5. METHODOLOGY
 First, the analyte should be dissolved in
a solvent making up to 0.1mg/ml and the
matrix should be dissolved with a
saturated or concentrated solution of
about 10mg/ml. Both the solution is then
mixed together in 1000:1 to 100,000:1
ratio.
 The mixture is placed on a metal target
plate which crystallizes on drying and
forms a solid deposit. Then the mixture is
transferred into the MALDI – TOF
instrument for analysis.

6.  Sublimation and ionization separate
the ions depending upon the size and
charge ratio through a TOF analyzer
which is operated on the MS software.
 To increase the ability in identifying
gram-positive and sugar non
fermenting bacterial species, formic
acid is used with the preparatory
extraction of microbes whereas gram-
negative bacteria can be identified
using direct cell profiling.

7. The process of mass
spectrometry

8. Target plate

9. APPLICATIONS OF MALDI-
TOF MASS SPECTROMETRY
 Biochemistry
 Peptide mass fingerprinting (PMF)
 Clinical and environmetal bacteriology
 Detection of viruses
 Organic chemistry
 Medicine

10. ADVANTAGES
 Significantly decreases the turnaround
time. Processing time is similar to
rapid bio-chemicals.
 The sample preparation is simple and
the sample requirement is minimal. A
single colony is sufficient in order to
generate spectra of sufficient quality
 Cost effective-low consumable costs

11.  Automated, robust, inter-laboratory
reproducibility
 Broad applicability (all types of
bacteria including anaerobes, fungi)
 Adaptable-open system, expandable
by user.

12. DISADVANTAGES
 Identification of new isolates is
possible only if the spectral database
contains peptide mass fingerprints of
the type strains of specific
genera/species/subspecies/strains
 No susceptibility information is
provided
 Not useful for direct testing of clinical
specimens (except urine)

13.  Some organisms require repeat
analysis and additional processing
(extraction)
 The acceptable score cut-offs vary
between studies and some closely
related organisms are not
differentiated.
 Some organisms currently cannot be
reliably identified by this method, such
as Shigella spp
and Streptococcus pneumoniae.

14. REFERENCES
 en.wikipedia.org/wiki/Matrix-
assisted_laser_desorption/ionization
 Modern Experimental Biochemistry. Rodney F Boyer.
Benjamin/Cummings publishing company Inc. Redwoodcity,
California.
 thesciencenotes.com/maldi-tof-mass-spectrometry-principle-
methodology-and-applications/