A 24-year-old male presents to a STD clinic with a single painless ulcer on external genitalia. The choice of laboratory test to look for the etiological agent would be –
Clues are:-


Painless ulcer
Single lesion


It may be either LGV or chance:-

Chancre  → Darkfield microscopy or serological tests (VDRL, FTA-ABS).
IGV → Demonstration of inclusion bodies, fries test, CFT.

Amongst all these tests only darkfield microscopy has been given in the options.
So, I am assuming that it is a case of primary syphilis (chancre), for which dark field microscopy can be used for diagnosis.
Scrappings from ulcer for culture on chocolate agar with antibiotic supplement
Serology from detection of specific IgM antibodies
Scrappings from ulcer for dark field microscopy
Scrappings from ulcer for tissue culture