Yet another variation of a respond-to mixin.

_respond-to.scss

// sass 3.2 or higher required
@mixin respond-to($min-width, $max-width: null) {
  $fix-mqs: false !default;

  // If we're outputting for a fixed media query set...
  @if $fix-mqs {
    // ...and if we should apply these rules...
    @if $max-width != null {
      @if (($fix-mqs >= $min-width) and ($fix-mqs <= $max-width)) {
        // ...output the content the user gave us.
        @content;
      }
    } @elseif ($fix-mqs >= $min-width) and $max-width == null {
      // ...output the content the user gave us.
      @content;
    }
  } @else {
    // Otherwise, output it using a regular media query
    $mq: "only screen and (min-width: #{$min-width})";

    @if $max-width{
      $mq: "#{$mq} and (max-width: #{$max-width})";
    }
    @media #{$mq} {
        @content;
    }
  }
}