Setting up nginx for socket-io and nodejs

I have a project which did not require socket-io till now, with following nginx configuration

server {
    server_name app.web.com;
    root /var/www/app/releases/current/public/;
    index index.html index.htm;

    access_log /var/log/nginx/app.access.log;
    error_log  /var/log/nginx/app.error.log;
    underscores_in_headers on;

    recursive_error_pages on;
    error_page 503 @maintenance;

    if (-f $document_root/system/maintenance.html) {
        return 503;
    }

    location @maintenance {
        error_page 405 = /system/maintenance.html;
        rewrite  ^(.*)$  /system/maintenance.html break;
    }

    location ~ ^/(js|css|images|media|system)/ {
        autoindex off;
        add_header Cache-Control public;
        expires 4w;
    }

    location / {
        try_files $uri $uri/index.html @proxy;
    }

    location @proxy {
        proxy_set_header Host $http_host;
        proxy_pass   http://127.0.0.1:7485;
    }
}

Now I have added a chat feature in it using socket-io. How do I add enable socket from nginx?