A report by Belgian newspaper Het Nieuwsblad that a minute camera was inserted into bike frames last weekend to search for motors was correct, Press Association Sport understands. None were found.
Czech Republic's Zdenek Stybar, who rides on the road for Mark Cavendish's Omega Pharma-QuickStep team, won the men's race in the non-Olympic discipline.
The women's race across the Dutch mud was won by home favourite Marianne Vos, the Olympic and world road race champion.
Cycling's world governing body has checked for motors in bike frames previously, but the weekend checks were the first time since disgraced rider Danilo Di Luca, a serial drug cheat, made claims of mechanical doping in an interview on Italian television last month.
In 2010, Swiss road racing star Fabian Cancellara had to fight off accusations of motor use following a dominant spring classics campaign when he won both the Tour of Flanders and Paris-Roubaix one-day races.
Scanners were brought in for the 2010 Tour de France and after winning the prologue in Rotterdam, Cancellara hit back at the claims.
Cancellara said: "After the race my bike was brought to the scanner and I told the guys there: 'Well, you better look at the engine. The engine's me'."