def fingerprint type=DEFAULT_FINGERPRINT
      core_fp = core.fingerprint type
      coating_fp = coating.collect{|c| c.fingerprint type}.flatten.uniq.compact
      (core_fp.empty? or coating_fp.empty?) ? [] : (core_fp+coating_fp).uniq.compact
    end
def fingerprint type=DEFAULT_FINGERPRINT
      core_fp = core.fingerprint type
      coating_fp = coating.collect{|c| c.fingerprint type}.flatten.uniq.compact
      (core_fp.empty? or coating_fp.empty?) ? [] : (core_fp+coating_fp).uniq.compact
    end
Get nanoparticle fingerprint (union of core and coating fingerprints)
 @param [String] fingerprint type
 @return [Array<String>]