Twitter CEO Jack Dorsey is selling his first tweet at auction, with bidding Saturday reaching $2 million in a sign of the appetite for virtual objects authenticated through blockchain technology."just setting up my twttr," Dorsey tweeted on March 21, 2006.On Friday he posted a link to "Valuables @Cent," an online marketplace for tweets where, the site says, investors or collectors can "buy and sell tweets autographed by their creators."The top bid Saturday for Dorsey's tweet — $2 million — came from Justin Sun, the founder of TRON, a platform for blockchain, the technology underlying cryptocurrencies. He also heads the BitTorrent streaming platform."The creator of a tweet decides if they would like to mint it on the blockchain, creating a 1-of-1 autographed version," Valuables explained.Buying 'a digital certificate'Buying a tweet means…