Rapid detection of antibiotics by Nanowire-Assisted Laser Desorption Ionization (NALDI) Mass Spectrometry

Owing to the misuse and overapplication of antibiotics both clinically and agriculturally, the gradual emergence of antibiotic resistance bacteria represents a major public health issue representing a $10 billion cost to clinics and countless deaths worldwide.  With few new antimicrobials expected in the coming years, it is of increasing importance for research and regulatory agencies to have access to an efficient method for detecting these small molecules.  Mass spectrometry has become an invaluable tool for the rapid identification of various compounds.  Laser Desorption/Ionization-Time of Flight (LDI-TOF) methods are particularly attractive for use with biological systems as they are “soft”, enabling the detection of sensitive compounds, and retain sensitivity within complex mixtures thus eliminating the need for timely separations and thus allowing high-throughput screens.  However, most LDI assays require low-molecular weight organic matrices that can interact with the target molecule and mask its detection (MALDI).  New nanowire-assisted methods (NALDI) eliminate these matrices, creating a new avenue for analyzing low-molecular weight compounds within biological systems both qualitatively and quantitatively.  In order to evaluate the efficacy of this method for detection of antibiotic compounds, we subjected 28 antibiotics of multiple classes to NALDI-TOF Mass Spectrometry.  Results show that six of these compounds are capable of reproducible detection, and in the case of Trimethoprim and Clindamycin down to the nanogram level.   Based on these results, NALDI-MS is an attractive candidate for a variety of high throughput assays relevant to the issue of antibiotic resistance.