Smartphone application developers, along with banks and merchants, have been in search of the mobile payment method that can "go viral."

Many apps are already available with payment functions, including various "wallet" apps -- Google Wallet, Square Wallet, Lemon Wallet. Others are waiting in the wings, including Flint and Clinkle, the latter a well-financed effort with the backing of Virgin Group founder Richard Branson. Apps for some coffee shops, including Starbucks, have payment features for your caffeine fix.

Among all these, Minh Tran is one independent developer who hopes he has the go-viral formula that will work.

Tran, 39, who several years ago launched an app, now called Fix311, for reporting potholes in a number of big cities, has a newer offering, CardSwapp Lite, for Android and Apple smartphones, that lets users make and take PayPal payments by scanning QR codes.

No extra hardware is needed on either end of the transaction.

Tran's free app has several functions. He introduced it in 2012 as a way to create and share electronic business cards, and for comparison shopping by scanning product bar codes.

The October-release version of the app includes the payment feature. In essence, Tran says, buyers needing to make a payment call up the CardSwapp app on their phones and scan the image of the seller's own CardSwapp QR code from their phone screen, or from an invoice or bill with the code printed on it. Type in an amount, and the transaction is completed through PayPal, whose users can make payments from cash accounts or credit cards.

In a restaurant, Tran said, you can pay "without giving your credit card to the waiter." Event planners could sell tickets by putting the bar code on a poster.

"What I've created is an app that can pay anybody," said Tran, who lives in Washington. "It's true peer-to-peer. I can pay you; I can pay my friend. I can pay anybody."

PayPal is working on its own version of a QR code payment scheme, due out next year, and the online payment company already has millions of users. But Tran hopes his multifunction app's head start will give him a chance to play in this big-stakes game.

If it doesn't, he says, he has had a patent pending on his system for several years. So, who knows?

(c) 2013 McClatchy News Service