Hoping to engage more than 300,000 people in a nationwide tour, a German-based biotech Saturday unveiled its Curiosity Cube science lab at Petco Park in one of the nation’s largest science expos. Petco was the first stop on the 12-month tour of the cube, a hands-on lab housed in a 22-by-10-foot shipping container retrofitted by MilliporeSigma, the North American arm of Merck KGaA, Darmstadt, Germany.