Ninguna moneda está respaldada por oro ni ningún otro metal.

What is the Bank’s “Promise to Pay”?
The words "I promise to pay the bearer on demand the sum of five [ten/twenty/fifty] pounds" date from long ago when our notes represented deposits of gold. At that time, a member of the public could exchange one of our banknotes for gold to the same value. For example, a £5 note could be exchanged for five gold coins, called sovereigns. But the value of the pound has not been linked to gold for many years, so the meaning of the promise to pay has changed. Exchange into gold is no longer possible and Bank of England notes can only be exchanged for other Bank of England notes of the same face value. Public trust in the pound is now maintained by the operation of monetary policy, the objective of which is price stability.

[Bank of England]

Is U.S. currency still backed by gold?
No, when the United States stopped selling gold to foreign official holders of dollars at the rate of $35 an ounce in 1971, it brought the gold exchange standard to an end. In 1973, the United States officially ended its adherence to the gold standard. Many other industrialized nations also switched from a system of fixed exchange rates to a system of floating rates. In August 1974, President Ford repealed the prohibition on the public's owning gold or engaging in gold transactions. Today, no country bans private ownership of gold.

[Federal Reserve Bank of Richmond]

After the United States suspended the gold convertibility of the dollar in 1971, a regime of flexible exchange rates emerged; in 1973, under that regime, the United States began to intervene in exchange markets on a more significant scale. In 1978, the regime of f lexible exchange rates was codified in an amendment to the IMF’s Articles of Agreement.

[The Federal Reserve System Purposes and Functions]