go get github.com/nanmu42/etherscan-api

import (
	"github.com/nanmu42/etherscan-api"
	"fmt"
)

func main() {
	// create a API client for specified ethereum net
	// there are many pre-defined network in package
	client := etherscan.New(etherscan.Mainnet, "[your API key]")
	
	// or, if you are working with etherscan-family API like BscScan
	//
	// client := etherscan.NewCustomized(etherscan.Customization{
	// Timeout:       15 * time.Second,
	// Key:           "You key here",
	// BaseURL:       "https://api.bscscan.com/api?",
	// Verbose:       false,
	// })

	// (optional) add hooks, e.g. for rate limit
	client.BeforeRequest = func(module, action string, param map[string]interface{}) error {
		// ...
	}
	client.AfterRequest = func(module, action string, param map[string]interface{}, outcome interface{}, requestErr error) {
		// ...
	}

	// check account balance
	balance, err := client.AccountBalance("0x281055afc982d96fab65b3a49cac8b878184cb16")
	if err != nil {
		panic(err)
	}
	// balance in wei, in *big.Int type
	fmt.Println(balance.Int())

	// check token balance
	tokenBalance, err := client.TokenBalance("contractAddress", "holderAddress")

	// check ERC20 transactions from/to a specified address
	transfers, err := client.ERC20Transfers("contractAddress", "address", startBlock, endBlock, page, offset)
}