Direct desorption and ionization. These techniques involve the application of laser energy, charged particles, or high electric fields to facilitate analyte desorption/ionization from individual cells, producing gas-phase ions suitable for MS detection under ambient and open-air conditions. Approaches include desorption electrospray ionization (DESI)-MS , easy ambient sonic-spray ionization, drop-on-demand inkjet printing with probe electrospray ionization (PESI)-MS, and laser-based methods such as laser ablation electrospray ionization (LAESI) 100, 101 , laser desorption/ionization droplet delivery (LDIDD) , and atmospheric-pressure MALDI (AP-MALDI) .