You are looking for Jack Blank and the Image Nation (also known as The Accidental Hero) by Matt Myklush.
The giant policeman is called Blue:
As the owner of the voice made his way upstairs, Jack saw that he was nothing less than a giant. The entire boat rocked from side to side as Blue walked up the steps. When he opened the door to exit onto the deck, he could barely fit through it. He was a ten-foot-tall hulking mass of muscle who looked like he could pick up every boat on the pier and juggle them if he wanted to. He wasn’t called Blue because he was a cop, but rather because his skin was a clear, bright shade of royal blue.
The girl is Allegra and she turns into liquid when she is frightened:
“Nice guy, huh?” Jack said to Allegra, who was tiptoeing her way out into the open.
“Eeep!” she yelped, and liquefied into a puddle again. She spilled across the floor and reformulated behind Prime, who tried and failed to repress an embarrassed sigh.
The character named Smart is Jonas Smart. He is just described as heartless because of his cold manner, but in fact he has no heart:
Years ago, I was diagnosed with a terminal heart condition. Countless transplant attempts failed, each one condemning me to die. A lesser man would have turned to despair, but I did not sit around waiting for a fatal heart attack to end my life. Using my TimeScope, I uncovered a cure perfected many years in the future and acted upon that information: I had my heart surgically removed.
After my heart was cut out of my chest, its functions were duplicated by a series of magnetic implants placed throughout my body. I now ingest iron-rich supplements that magnetize my blood and circulate it through my veins. A radical solution, to be sure, but no one can argue with the results.
The maglev roads were invented by Smart's company:
The biggest company in the world,” Jazen answered. “They do business all around the globe, but under a lot of different fake names. You’d be amazed at who some of their front companies are. Tangitals and Hard-Light Holos were invented by the owner of the company, a man named Jonas Smart.”
“He also invented HoverPads, SmartCams, MagLev roads, and a ton of other things,” Blue added. “In addition to being the senior member of Empire City’s Inner Circle, he also runs SmartCorp. These days, that means he pretty much runs Empire City.”